P2 Revision Booklet

Momentum

Medium (Grade C)

Q1.          (a)     A car is being driven along a straight road. The diagrams, A, B and C, show the horizontal forces acting on the moving car at three different points along the road.
Describe the motion of the car at each of the points, A, B and C.

(3)

(b)     The diagram below shows the stopping distance for a family car, in good condition, driven at 22 m/s on a dry road. The stopping distance has two parts.
(i)      Complete the diagram below by adding an appropriate label to the second part of the stopping distance.

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(1)

(ii)     State one factor that changes both the first part and the second part of the stopping distance.
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(1)

(c)     The front crumple zone of a car is tested at a road traffic laboratory. This is done by using a remote control device to drive the car into a strong barrier. Electronic sensors are attached to the dummy inside the car.

 
(i)      At the point of collision, the car exerts a force of 5000 N on the barrier.
State the size and direction of the force exerted by the barrier on the car.
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(1)

(ii)     Suggest why the dummy is fitted with electronic sensors.
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(1)

(iii)    The graph shows how the velocity of the car changes during the test.

Use the graph to calculate the acceleration of the car just before the collision with the barrier.
Show clearly how you work out your answer, including how you use the graph, and give the unit.
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                           Acceleration = ............................................................
(3)
(Total 10 marks)
Q2.          (a)     The diagram shows a car travelling at a speed of 12 m/s along a straight road.

(i)      Use the equation in the box to calculate the momentum of the car.
 
momentum = mass × velocity	

         Mass of the car = 900 kg
         Show clearly how you work out your answer.
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Momentum = .............................. kg m/s
(2)

(ii)     Momentum has direction.
         Draw an arrow on the diagram to show the direction of the car’s momentum.
(1)

(b)     The car stops at a set of traffic lights.
          How much momentum does the car have when it is stopped at the traffic lights?
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Give a reason for your answer.
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(2)
(Total 5 marks)
 Momentum-Mark scheme

M1.          (a)     A constant speed / velocity
accept steady pace
do not accept terminal velocity
do not accept stationary
1

B acceleration
accept speeding up
1

C deceleration
accept slowing down
accept accelerating backwards
accept accelerating in reverse
do not accept decelerating backwards
1

(b)     (i)      the distance the car travels under the braking force
accept braking distance
1

(ii)     speed/velocity/momentum
1

(c)     (i)      5000 (N) to the left
both required
accept 5000(N) with the direction indicated by an arrow drawn pointing to the left
accept 5000(N) in the opposite direction to the force of the car (on the barrier)
accept 5000(N) towards the car
1

(ii)     to measure/detect forces exerted (on dummy / driver during the collision)
1

(iii)    4
allow 1 mark for showing a triangle drawn on the straight part of the graph
or correct use of two pairs of coordinates
2

m/s2
do not accept mps2
1
[10]
 M2.          (a)     (i)      10800
allow 1 mark for correct substitution i.e. 900 × 12
2

(ii)     arrow pointing towards the left
allow anywhere on the diagram or at bottom of the page
1

(b)     zero
accept 0 / none / nothing
1
          velocity is zero
accept speed for velocity
accept stopped / not moving
accept a calculation i.e. 900 × 0 = 0
1
[5]