02 - Mechanics

Question 1

At high speeds the guide pin may become disengaged from the groove.
Use Newton’s first law to explain why the car would then leave the track at a corner.

Answer 1

No Resultant Force is Acting on the Car

Car continues moving in straight line

Question 2

Suggest why the actual speed of the car is less than the calculated speed

Answer 2

Energy is dissipated to heat due to friction between the wheels and track

Question 3

State what is meant by work done

Answer 3

Force x Distance moved in the direction of the applied force

Question 4

A projectile would have a greater range on the Moon than the Earth because of the lower gravitational field strength and because of the lack of an atmosphere.

Explain how each of these factors would increase the range of the projectile.

Answer 4

Lower Gravitational Field Strength:
lower acceleration so an increased time of flight

Lack of atmosphere:
no work done against friction

Question 5

Explain why the string would not become horizontal, however great the acceleration

Answer 5

String always has a weight so tension needs a vertical component.

Question 6

Suggest why many devices contain 3 accelerometers, arranged at right angles to each other.

Answer 6

to detect movement in x,y,z planes

Question 7

Demonstration-
Large 7kg bowling ball pendulum on a long piece of wire released from nose of student

Precautions-
Don’t push ball - just release
Don’t move face b4 ball returns

Explain this demonstration and the need for the precautions.

Answer 7

Demonstration-
Total energy of the pendulum is conserved as energy transfers from GPE to KE vice versa
It cannot move higher than its starting point because that would require extra GPE
Energy is lost against air resistance so will stop the pendulum reaching its starting point

Precautions-
Pushing provides extra energy making the pendulum move higher so it will hit the student.
if the face moves forwards the ball may reach it.

Question 8

Suggest a reason for inefficiency

Answer 8

friction

Question 9

Suggest why a rubber band is used to support the arm

Answer 9

so that it can store elastic potential energy

Question 10

state the energy transfers that occur when the string is released

Answer 10

Elastic Potential Energy
to
GPE + KE + Thermal Energy

Question 11

explain why the distance increases as the angle of a projectile increases

Answer 11

the greater the angle the greater the tension
the greater the acceleration of the projectile
greater velocity of the projectile
s = ut linked to a greater range

Question 12

state why replacing a projectile with a lower mass can increase the range of the projectile

Answer 12

F=ma

reduced mass increases acceleration for the same force applied on the projectile

Question 13

Suggest one modification to the model that would also increase the range of the
projectile. Give a reason for your answer

Answer 13

increase tension by adding more rubber bands or stiffer rubber bands
increase vertical distance by increasing arm length or raising the device

Question 14

Describe the energy transfers of a bungee jumper

Ignore any
changes that could be due to air resistance

Answer 14

Freefall > GPE TO KE
deceleration as the bungee rope stretches > GPE AND (KE TO EPE)
upwards motion as the bungee rope contracts > EPE TO (GPE AND KE)

Question 15

The student stated that as long as the opposite poles of the magnets are facing one
another, the attractive force created should cause the toy car to start moving forward.

Explain why in practice this could never work.

Answer 15

Due to Newton’s 3rd Law, magnet A exerts a force on magnet B and magnet B exerts an
equal and opposite force on magnet A
The magnets are connected to the same body/each other
There will be no resultant force as the forces will balance

Question 16

Suggest and explain a measure that a swimmer could use to reduce
the drag force acting on him

Answer 16

Wear tight fitting clothes- reduce turbulent flow

or

Keep their body as flat as possible - cross sectional area as small as possible

Question 17

State and explain the effect on the motion of the iceberg if the tow ropes were
longer. Assume that the tug boat’s power output is constant.

Answer 17

No effect on the motion, the iceberg will travel at the same speed.
Resultant tension is the same

Question 18

Explain how a lawnmower with the top section of the handle horizontal changes the minimum force required to push the lawnmower.

Answer 18

Force is in direction of motion so that less force needs to be applied

Question 19

Kinetic energy of the wind is transferred to
electrical energy by the turbine as the blades rotate.

Explain why we can say that the wind is doing work on the blades.

Answer 19

Wind exerts a force on the blades, the

blades move through a distance in the direction of the force

Question 20

Suggest a reason why it is not possible to usefully transfer 100% of the kinetic
energy of the wind on a wind turbine

Answer 20

Not all the air hits the blades

Question 21

Suggest the limitations of using wind turbines to provide power

Answer 21

Wind doesn’t always blow, if there is no wind they don’t work as turbines need a minimum amount of wind to generate the electricity

need a large amount of wind

can’t be used in very high winds

Low power output so need a lot of turbines which take up a lot of space

Question 22

Explain reasons why the projectile does not go as far as expected

Answer 22

Air resistance
Friction
Less energy has been transferred to the projectile

Question 23

2. An object is falling at TERMINAL VELOCITY

Answer 23

The acceleration of the object is zero
There is a resistive force acting on the object
The object has weight

Question 24

2. A space rocket lifts off vertically because

Answer 24

the exhaust gases exert a force on the rocket

Question 25

2. Suggestion:
   In her experiment , u is directly proportional to root s and is independent of the mass of the coin

Discuss validity of suggestion

Answer 25

v^2=u^2+2as
v=0 so u= root (-2as)
a is a deceleration caused by friction
F=ma
F=km=ma so a must be constant
so acceleration a is the same so statement is correct

Question 26

2. State what is meant by the centre of gravity of an extended body

Answer 26

the point through which the weight of a body acts

Question 27

2. Comment:
   if the silk thread can withstand a tension equal to the weight of the spider then this safety system should work

Deduce validity

Answer 27

F+mg=ma
(the tension will equal the mass of spider x acceleration as the thread brings the spider’s fall to a stop) + weight of spider so is incorrect

Question 28

2. State assumption made in calculating the initial acceleration from rest

Answer 28

neglect friction

Question 29

2.Give reasons why solar power alone wouldn’t be suitable for a family car