Past papers- 1. forces, motion and energy

Question 1

The density of steel is 7800kg/m3 and the density of water is 1000kg/m3. Explain why the ship floats in the water.

The containers with the greatest mass are loaded near the bottom of the ship. State and explain the effect on the stability of the ship of loading the containers in this way

Define the unit kWh

Answer 1

ship is not solid steel / there are air spaces in ship (average) density of ship is less than the density of the water

the centre of gravity is lower and so the ship is more stable

energy transferred in one hour at a rate of transfer of 1 kW

Question 2

Describe what happens to the velocity of the motorcyclist as she travels around the bend at constant speed.

Explain why there must be a resultant force on the motorcyclist as she travels around the bend.

Answer 2

1. (velocity) changes (as direction of motion changes) OR direction (of velocity) changes
2. because there is an acceleration / change in velocity / change in direction / change in momentum (which needs a
   resultant force)

motorcyclist accelerates / changes momentum (because velocity / direction changes)

(resultant) force is perpendicular to the motion (of the motorcycle) OR a∝F

Question 3

Explain, in terms of forces, the changes in motion which occur from when the parachutist leaves the hot-air balloon

Answer 3

(initially there is acceleration due to) weight OR gravitational force OR unbalanced force / resultant force / downward force

(then) air resistance increases as speed or velocity increases

(as air resistance increases) resultant force downwards decreases OR acceleration decreases

constant speed when air resistance = weight / gravitational force

Question 4

As the student catches the ball, she moves her hands backwards. Explain the effect of this action on the student’s hands.

Answer 4

longer time (of impact / contact) AND smaller force (on them)
OR
longer time (of impact / contact) AND does not hurt as much

Question 5

State and explain whether each of the following methods of electrical power generation is renewable.

(i) power generation in a nuclear power station

(ii) power generation from waves in the sea

Answer 5

non-renewable- (nuclear) fuel is used up

renewable- waves will always continue OR produced by wind which will always continue OR nothing used up

Question 6

Explain how speed-time graph shows that there is no resultant force

Answer 6

• Line on graph is horizontal / gradient is zero
• (therefore) no acceleration / speed is constant
• (resultant) force causes / is proportional to acceleration

Question 7

State two environmental benefits of the electrically powered bicycle

Answer 7

less noise OR no noise

less OR no air / gaseous pollution (from the bicycle) OR does not produce acid rain

(the bicycle) uses no / less fossil fuel

does not contribute to greenhouse effect OR does not release CO2

Question 8

Suggest why, in normal use, the car needs to be recharged after travelling less than 390km.

Answer 8

(repeated) acceleration / deceleration / use of brakes /varying speed
motion uphill / uneven road surface
cold weather / headwind

Question 9

State one disadvantage of hydroelectric power schemes.

State all renewable source of energy

State all sources which derives its energy from the Sun.

Answer 9

damage to habitats (for fish) / construction is expensive / droughts / flood risk if dam bursts

hydroelectric/ biofuel / wind / geothermal / tidal / solar / wave

• fossil fuel / named fossil fuel
• biofuel / wood / crops
• hydro
• wave
• wind
• solar cell / panel

Question 10

Both of the blocks now move at a constant speed of 0.60m/ s until block B hits the
ground and the thread becomes loose.
Explain the energy change that takes place in block A after block B stops moving

Answer 10

kinetic energy (of block A) decreases

thermal / internal energy produced / increases (due to friction)

friction mentioned or block slows down / decelerates

Question 11

State what is meant by the limit of proportionality

Answer 11

beyond where the extension is not directly proportional to the load or (point) where extension stops being directly
proportional to the load or point up to which extension is directly proportional to the load

Question 12

Describe how to use a stop-watch to determine the time period of the pendulum.

Answer 12

(use stop-watch to) time oscillations

(use of fiduciary) aid to determine a complete cycle

(use of) multiple oscillations AND division (to determine period)

Question 13

State what is meant by the moment of a force about a point.

Define the moment of a force.

Answer 13

(moment of a force) is the turning effect (about a point / pivot)

force × perpendicular distance from pivot / point

Question 13

State one advantage and one disadvantage of tidal power as an energy resource.

State the main source of energy for tidal energy

Answer 13

advantages:
* renewable
* reliable or predictable
* running cost low
* does not produce (harmful) pollution.

disadvantages:
* (high) cost of construction
* possible effects on (marine) life
* not available all day
* power produced doesn’t always match with peak demand
* limited number of sites
* maintenance difficult /increased corrosion (because underwater).

Moon

Question 14

The power station uses some of its waste thermal energy to heat water for houses in a nearby
town. State one problem of using waste energy in this way if the power station is far from the town.

Suggest a way of reducing this problem

Answer 14

water will cool (too much) / thermal energy lost (during transfer)

lag/insulate (pipes) OR transport in a poor conductor of thermal energy

Question 15

State environmental consequences of burning coal to generate electricity.

Answer 15

• air pollution / harmful gases / acid rain
• CO2 / greenhouse gases / contribution to global warming
• not renewable
• damage from mining / drilling or any valid environmental consequence of transport of coal

Question 16

Explain, in terms of the forces acting on the skydiver as he opens his parachute

Explain why opening the parachute cannot reduce the speed of the skydiver to zero

Answer 16

1. (deceleration because) upward force greater than weight or upward resultant force

air resistance decreases (with decreasing speed / with time)
or deceleration decreases or resultant (upward) force decreases

(until / finally) weight equals air resistance or forces balance or at terminal / constant velocity / speed

2. at zero speed there is no air resistance
   weight / downwards force is (still) acting or there is (now) a resultant force (downwards at zero speed)

OR

forces balance at a speed greater than zero
speed cannot decrease / no deceleration once forces balance

Question 17

As the trolley moves across the rough surface, it slows down and stops. Explain, in terms of the work done, the energy change that takes place as the trolley slows down.

Answer 17

work done against / due to / because of friction or kinetic energy (of trolley) used to do work

kinetic energy decreases (to zero)

thermal energy produced

Question 18

Explain why the pump must exert an increasing pressure on the oil as the depth of the oil increases

Answer 18

pressure due to increased height of oil in cylinder or pressure in liquid increases as depth increases

to keep the upwards force constant or to lift the (extra) oil
or to counteract / oppose the increased pressure / force / weight of the oil

Question 19

Explain, in terms of the momentum of the molecules, why there is a pressure at the inner surface of the balloon.

Explain why the volume of the air in the balloon decreases as the temperature decreases.

Answer 19

they / molecules collide with inner surface
momentum (of a molecule) changes / reverses
force exerted / impulse
force spread over area / surface or p =F / A

molecules move more slowly / have less kinetic energy
pressure (inside balloon) decreases or pressure is directly proportional to temperature or p∝T
volume is directly proportional to temperature or V∝T
molecular collisions less frequent
molecular collisions less violent / hard / exert smaller impulse
water / external pressure compresses balloon or
water pressure greater (and balloon compressed)

Question 20

The train took 80s to reduce its speed from 84m/s to 42m/ s. Explain why, with the same braking force, the train takes more than 80s to reduce its speed from 42m/ s to zero.

Answer 20

less drag / air resistance (at slower speeds)

Question 21

The angle the bus makes with the horizontal is gradually increased until the bus begins to topple to the left.
Explain why the bus begins to topple.

There are 30 passengers in the upper compartment of the bus and 2 passengers in the bottom compartment of the bus. State how this affects the stability of the bus and the reason for this

Answer 21

a. line of action of the centre of mass falls outside the base of the bus
anticlockwise moment is greater than clockwise moment

b. bus more likely to fall over / topple / less stable
(line of action of) centre of mass may fall outside (the base of) the bus

Question 22

Suggest why some of the kinetic energy of the air that passes through the circular area swept out by the blades is not converted into electrical energy.

Answer 22

Speed of air not reduced to zero (in passing through turbine) OR some air passes through blade area without change of speed OR without hitting blades
OR not all k.e. of air transfers to blades
OR air retains some of its k.e.
OR friction in bearings of blades

Question 23

State three ways in which a force may change the motion of the object.

Answer 23

Accelerate or increase speed OR Decelerate or decrease speed OR Change speed

Change direction OR causes rotation

Question 24

State the principle of the conservation of momentum.

Explain how the principle of the conservation of momentum applies to the accelerating rocket and the exhaust gases.

Answer 24

i. no external forces OR isolated system
sum of momenta / (total) momentum remains constant

ii. rocket gains (upward) momentum

(ejected) gas gains equal (quantity of) momentum in opposite direction OR momentum of gas decreases by equal amount

Question 25

State what is meant by centre of mass.

The concrete block is removed. The sign and support post rotate about point P in a clockwise
direction. State and explain what happens to the moment about point P due to the weight of the sign as
it rotates.

Answer 25

(the point) where (all) the mass can be considered to be concentrated

(moment / it) increases
perpendicular distance (between P and line of action of) W increases

Question 26

State and explain, in terms of molecules, any change in the pressure of a gas when the volume is reduced at a constant temperature.

Answer 26

pressure increases

• molecules travel shorter (average) distance between collisions with walls NOT molecules change speed
• molecules hit walls more often

OR more collisions (per unit area) with walls
* {greater force OR greater (rate of) change of momentum of molecules} per unit area on walls

Question 27

The brakes of the model are released. State and explain the direction of the acceleration of the model

State and explain any change in the magnitude of the initial acceleration if the brakes are first released when the tank is nearly empty

Answer 27

1. (acceleration is) to right/backward
   Explanation: force (from water OR on model) to right /backwards OR acceleration in same direction as
   force (from water OR on model)
2. (acceleration) more (when empty)
   mass less (and force is constant) as F=ma / Newton’s 2nd law / change in momentum

Question 28

Dock walls sometimes have the pillars replaced with rubber car tyres. Explain how this reduces the possibility of damage when a boat docks.

Answer 28

smaller force (on dock/ship) because increases time of collision OR increased distance of collision (on the dock/ship)

Question 29

Define impulse

Answer 29

force × time (for which it acts)

Question 30

Describe how the molecular structure of the liquid metal differs from that of the solid metal.

Answer 30

(molecules /they) have an irregular arrangement / not ordered/random arrangement
(molecules /they) are (slightly) further apart (on average)
(molecules /they are) not fixed in place

Question 31

arrangement and forces in solid, liquid & gas

Answer 31

Solids – molecules in lattice arrangement
solids – strong forces between molecules

liquids – molecules not fixed in place OR molecules have an irregular arrangement OR molecules (slightly) further apart (on average) than in solids OR spaces between the molecules
liquids – (average) forces too weak to keep molecules in a definite pattern OR forces just enough to hold molecules in the bulk of the liquid

gases – molecules far apart
gases – weak / no forces between molecules (except during collisions)

Question 32

Explain why the gravitational potential energy (g.p.e.) of the object increases with height

Answer 32

(Because g.p.e. is) the work done by the force
OR the force × the distance that the object rises
OR mgh and height is greater

Question 33

movement of the molecules in solid and gas

Answer 33

(Molecules) vibrate

random/haphazard/in all directions AND
with high speed
freely
zig-zag
in straight lines

Question 34

The actual height reached by the bullet is less than the value calculated. Explain, in terms of the forces acting on the bullet, why this is so

As the bullet rises through the air, its kinetic energy decreases. State what happens to this energy

Answer 34

(force of) air resistance acts downwards
adds to gravitational force/resultant force increases/deceleration increases/deceleration > g

(kinetic energy) to gravitational potential energy
(kinetic energy) to thermal/internal energy

Question 35

State the conditions which must be true if the object

(i) does not accelerate
(ii) does not rotate.

Answer 35

No resultant force /net force OR Forces are balanced OR Forces in opposite directions are equal OR Forces cancel

no resultant/ net moment / torque/turning effect
OR (Sum of) clockwise moments = (sum of) anticlockwise moments

Question 36

Suggest one reason why there is a delay before the temperature of the water increases to 23 °C as surrounding air increases to a temperature above 23 °C.

Explain why, after this delay, bulb B sinks. Assume the bulbs do not expand

Answer 36

Glass is a poor conductor of heat OR glass conducts heat at a slow rate OR water has a high (specific) heat capacity

The water expands OR separation of water molecules increases , The water becomes less dense , Bulb B now has a greater density than the water (and sinks) OR Weight of bulb B more than buoyancy forces /upthrust

Question 37

State what is meant by the term weight.

Explain what is meant by mass.

difference bw the two

Answer 37

(Weight is) force/pull of gravity (acting on an object)

(Measure of) quantity / amount of matter OR (property) that resists change in motion / speed / momentum
OR measure of a body’s inertia

weight has direction / mass does not
weight is a vector / mass is not
weight varies / mass does not
mass is amount of matter
weight is a force / mass is not

Question 38

Describe a process by which electrical energy is obtained from the chemical energy stored in this fuel.

Explain why the Sun is the source of the energy stored in the fuel.

Explain whether the process in (a) is renewable

Answer 38

any three from five:
* thermal energy / heat (from fuel)
* water / steam / gas heated OR steam produced
* (steam / gas) turns / moves / drives turbine
* (turbine) turns / moves / drives generator
* 2 correct energy transfers

sun is energy source for plants / living matter (to grow)
plant / animal (remains compressed) into fuel OR carbon / chemical energy stored / trapped in plant / animal (remains)

not renewable (as fuel is consumed)
could only be replaced over very long time period (e.g. clearly > 50 years)

Question 39

Describe and explain a danger to a driver of not wearing a safety belt during a sudden stop.

Answer 39

(Without seat belt, driver:) e.g. keeps moving (forwards)/ does not stop/ has inertia/ has momentum

(Driver) hits steering wheel/windscreen/ dashboard

Question 40

The deceleration of the dummy is less than the deceleration of the passenger compartment. Explain why this is of benefit for the safety of a passenger.

Answer 40

Force/ impact on passenger or dummy less (than without seat belt/airbag)
Passenger less likely to be injured/ hurt/ damaged

Question 40

Suggest why the skier bends his body

Answer 40

to reduce (air) resistance/ drag OR
to lower centre of mass

to increase acceleration/ speed/resultant force OR smaller (frontal) area/ better aero(dynamic) shape OR to improve
stability / balance

Question 41

The force needed to open the lid in water is not equal to the value calculated. Suggest two reasons for this.

Answer 41

weight of lid
(there is a) pressure inside box
OR upthrust on lid
moment of force changes
friction (of hinge)
drag of water

Question 42

Explain the benefit of increasing the time of contact for the people in the car

Answer 42

(increased time causes) decreased rate of: change of momentum/acceleration/deceleration/impulse ÷ time

smaller forces on people/less injury

Question 43

The tanker sails out onto a calm sea. The density of sea-water is greater than the density of
river water. State and explain any change in the depth of the bottom of the tanker below the surface.

Answer 43

Weight of tanker has to be equal to upward force of water
Depth (below surface) is /becomes less OR Tanker rises
(Tanker rises) because pressure /force on bottom of tanker
is greater OR because upthrust greater
OR At same depth as in river, pressure / force on bottom of
tanker is higher so tanker rises

Question 44

State one advantage and one disadvantage of generating electrical power in nuclear power stations compared with electrical power generated using wind turbines

Answer 44

advantage – one from:
* Continuous supply of energy
* not affected by the weather OR not affected by wind strength
* produces large amounts of energy

disadvantage – one from:
* resources finite / not renewable
* cost / difficulty of building / cost / difficulty of decommissioning
* danger if any leak of radiation
* produces hazardous / dangerous waste OR difficulty of storage of used radioactive material OR nuclear waste must be stored for a long time

Question 45

State two renewable sources of energy.
Source 1 ………………………………………………..
Source 2 ………………………………………………..

(ii) State one social, economic or environmental disadvantage of one of your answers to

Answer 45

solar, wind, water, hydroelectric, waves, tidal, geothermal

Energy for wind / waves / Sun not always available
Cost of building wind turbines or tidal barrages or hydroelectric dams
Wind turbines affect the scenery of some areas
Solar (farms) use (agricultural) land / takes up a lot of space

Question 46

(a) Describe a renewable process by which electrical energy is obtained from the energy stored
in water. You may draw a diagram in the space.

(b) Explain why the process described in (a) can be regarded as renewable.

(c) Explain whether the Sun is the source of the energy stored in the water in (a).

Answer 46

Hydroelectric
8(a) Hydroelectric named OR water from behind dam
K.E. of (falling) water used / P.E. of stored water
Turbine / waterwheel / paddle wheel operated
(Turbine) turns / drives a generator (that produces electricity)

8(b) Rain (fills lakes in high places)
Cause of rain is the Sun, so renewable

8(c) Sun evaporates water from sea etc. to fall (later) as rain
Sun is the source of energy.

Tidal flow
8(a) Tides / tidal flow named
K.E. of water used
Turbine / waterwheel / paddle wheel operated
(Turbine) turns / drives a generator (that produces electricity)

8(b) Moon (and Sun) causes tides
Moon (and Sun) permanently in place, so renewable

8(c) Attraction due to Moon’s (and Sun’s) gravity causes tides
Sun is a source of (part of) the energy OR Sun is not the primary source of energy

Question 47

The use of wind turbines on a large scale has environmental and economic impacts. Describe one environmental impact and one economic impact.

Answer 47

relevant environmental pro or con, e.g. no /less air pollution, no / less greenhouse gases OR visual / noise
impact / pollution, injure birds,
deforestation, conserves non-renewables
relevant economic pro or con, e.g. no fuel cost or expensive to install (compared to other types of generation)