G841 Legacy Papers

Question 1

State why the equation F=ma cannot be applied to particles travelling at speeds very close to the speed of light

Answer 1

the MASS of particles increases (at its speed gets closer to the speed of light)

Question 2

Explain why we cannot use the equation v=u+at to predict the velocity of a car at a later time even when the forward force is constant

Answer 2

The drag force changes with speed/ acceleration is not constant

Question 3

Describe how Global Positioning System (GPS) is used to locate the position of a car on the Earth’s surface

Answer 3

1. Several SATELLITES used
2. Distance from (each) satellite is determined
3. Position/distance is determined using c/speed of e.m waves and delay time
4. Trilateration is used to locate the position of the car

Question 4

How does greater speed affect braking distance?

Answer 4

distance is directly proportional to speed squared

Question 5

How does a greater mass increase braking distance?

Answer 5

distance is directly proportional to mass

Question 6

How do tyres/brakes affect braking distance?

Answer 6

Worn brakes/tyres implied less friction therefore greater distance

Question 7

How do road conditions affect braking distances?

Answer 7

Wet/slippery/icy roads mean less friction therefore greater distance

Question 8

Explain why the tension in a cable is different when the object is accelerating upwards

Answer 8

The tension would be greater than the weight
Explanation in terms of resultant/net force=ma

Question 9

State why the magnitude of the resuotant velocirt of the balloon is not the sum of the speeds of the balloon and the wind

Answer 9

Velocity is a vector so it also has direction

Question 10

A student investigates wires of the same material and same length. A is thicker than B. Explain which of these wires has a greater value of force constant

Answer 10

For the SAME force, A has a smaller extension
A has the greater force constant

Question 11

Describe the energy changes of a spring attached to a block as it falls to the ground (and touches it)

Answer 11

GPE AND KE OF THE BLOCK DECREASES (not the spring as it has negligible mass)
STRAIN/EPE in spring increases (GPE and KE converted to EPE)
when touches ground, no KE, spring has MAXIMUM STRAIN/EPE

Question 12

Explain the motion of a skydiver immediately after jumping

Answer 12

Only force is weight
Drag is 0
Net force=weight
Acceleration=g/9.81

Question 13

Explain the motion of a skydiver at a time before terminal velocity is reached

Answer 13

Drag increases with speed (d prop. to s^2)
Net force decreases, weight>drag
Acceleration less than g

Question 14

Explain the motion of the skydiver at terminal velocity

Answer 14

Weight=drag, net force=0
Acceleration=0, constant velocity

Question 15

At terminal velocity, falls at constant speed. Kinetic energy does not change even though decreases in GPE. State what happens to this loss of GPE

Answer 15

transferred to heat/thermal energy

Question 16

What would happen to a vt graph if a heavier skydiver fell?

Answer 16

Terminal velocity increases
Initial gradient/slope is equal to g
Time taken to reach terminal v is longer

Question 17

State the principle of moments

Answer 17

For equilibrium of an object the sum of CW moments about a point= sum of ACW moments about same point

Question 18

Define the ultimate tensile strength of a material

Answer 18

The maximum tensive stress a material can withstand before breaking

Question 19

Define velocity

Answer 19

Rate of change of displacement

Question 20

Briefly describe how the air bag is triggered and how it minimises the impact force on the driver

Answer 20

A large deceleration/decrease in speed triggers bag
It prevents collision with the wheel/dashboard
It increases time/distance
Results in a smaller deceleration of the person

Question 21

Define work done by a force

Answer 21

Force x perpendicular distance moved in the direction of motion

Question 22

True or false: in a vacuum, a 2kg object will fall faster towards the ground than a 1kg object

Answer 22

False
All objects falling towards Earth in a vacuum have the same acceleration

Question 23

Define a couple

Answer 23

A pair of equal and opposite forces with their lines of action separated by distance

Question 24

Cair is brought to rest by applying brakes. Explain whether the distance travelled by a car before it stops is greater than, equal to or less than the distance travelled on a horizontal road

Answer 24

Distance is greater
There is a COMPONENT of weight down the slope/against resistive force
NET force is less/magnitude od deceleration smaller

Question 25

State two factors that affect the acceleration of an object

Answer 25

Mass and net force (f=ma)

Question 26

After opening their parachute, the skydiver reaches a lower terminal velocity. Describe and explain how the magnitude of the deceleration of the skydiver changes as their velocity reduces.

Answer 26

When opened,Drag increases/D>W
Drag decreases as speed decreases (net force decreases)
Magnitude of deceleration decreases