8 Newton’s laws of motion
Exam-style questions
AQA Physics
1
A car, of mass 970 kg, is travelling at 15 m s–1 along a level road when its driver
performs an emergency stop. The car’s braking system applies a constant
braking force of 6.1  103 N to the car. Assume that the braking force is the
resultant force acting on the car.
a Calculate the distance the car moves in coming to a halt during an
emergency stop.
distance
m (4 marks)
b The car is now loaded with passengers and luggage and again travels at
15 m s–1. State and explain how this affects the braking distance of the car.
Assume that the car experiences the same braking force as in part a.
(3 marks)
From AQA Physics B PHYB2 Physics Keeps Us Going January 2012 (Question 10)
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8 Newton’s laws of motion
Exam-style questions
AQA Physics
2
Figure 1 shows a sledge moving down a slope at constant velocity.
The angle of the slope is 22°.
Figure 1
The three forces acting on the sledge are weight, W, friction, F, and the normal
reaction force, R, of the ground on the sledge.
a
With reference to an appropriate law of motion, explain why the sledge is
moving at constant velocity.
(2 marks)
b The mass of the sledge is 4.5 kg. Calculate the component of W
i parallel to the slope
ii
perpendicular to the slope.
(2 marks)
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2
8 Newton’s laws of motion
Exam-style questions
AQA Physics
c
State the values of F and R.
F
R
(2 marks)
From AQA Physics A PA02 Mechanics and Molecular Kinetic Theory June 2008
(Question 2)
3
In the 1969 Moon landing, the Lunar Module separated from the Command
Module above the surface of the Moon when it was travelling at a horizontal
speed of 2040 m s–1.
To descend to the Moon’s surface, the Lunar Module needed to reduce its speed
using its rocket as shown in Figure 2.
Figure 2
a
i
The average thrust from the rocket was 30 kN and the mass of the Lunar
Module was 15 100 kg.
Calculate the horizontal deceleration of the Lunar Module.
horizontal deceleration
ii
m s–2 (2 marks)
Calculate the time for the Lunar Module to slow to the required horizontal
velocity of 150 m s–1. Assume the mass remained constant.
time
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s (2 marks)
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8 Newton’s laws of motion
Exam-style questions
AQA Physics
b The rocket was then used to control the velocity of descent so that the Lunar
Module descended vertically with a constant velocity as shown in Figure 3.
Due to the use of fuel during the previous deceleration, the mass of the
Lunar Module had fallen by 53%.
Figure 3
i
ii
Draw force vectors on Figure 3 to show the forces acting on the Lunar
Module at this time. Label the vectors.
Calculate the thrust force needed to maintain a constant vertical
downwards velocity.
thrust
c
(2 marks)
N (2 marks)
When the Lunar Module was 1.2 m from the lunar surface, the rocket was
switched off. At this point the vertical velocity was 0.80 m s–1. Calculate the
vertical velocity at which the Lunar Module reached the lunar surface.
vertical velocity
m s–1 (2 marks)
From AQA Physics A PHYA2 Mechanics, Materials and Waves January 2011
(Question 5)
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4
8 Newton’s laws of motion
Exam-style questions
AQA Physics
4
An aircraft accelerates horizontally from rest and takes off when its speed is
82 m s–1. The mass of the aircraft is 5.6  104 kg and its engines provide a
constant thrust of 1.9  105 N.
a Calculate
i the initial acceleration of the aircraft,
(1 mark)
ii
the minimum length of runway required, assuming the acceleration is
constant.
(2 marks)
b In practice, the acceleration is unlikely to be constant. State a reason for this
and explain what effect this will have on the minimum length of runway required.
(2 marks)
c
After taking off, the aircraft climbs at an angle of 22° to the ground. The thrust
from the engines remains at 1.9  105 N. Calculate
i the horizontal component of the thrust
(1 mark)
ii
the vertical component of the thrust.
(1 mark)
From AQA Physics A PA02 Mechanical and Molecular Kinetic Theory January 2008
(Question 5)
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5
8 Newton’s laws of motion
Exam-style questions
AQA Physics
5
A ball bearing is released into a tall cylinder of clear oil. The ball bearing initially
accelerates but soon reaches terminal speed.
a By considering the forces acting on the ball bearing, explain its motion.
(3 marks)
b How would you demonstrate that the ball bearing had reached terminal speed?
(2 marks)
From AQA Physics A PA02 Mechanics and Molecular Kinetic Theory January 2002
(Question 7)
6
Figure 6 shows a car that travels down a hill of constant slope with the engine
turned off. The slope is inclined at 9° to the horizontal.
Figure 6
a
The total mass of the car is 1200 kg.
i Show that a force of about 1.8 kN acts down the slope due to the weight
of the car.
(2 marks)
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8 Newton’s laws of motion
Exam-style questions
AQA Physics
ii
The car is travelling at a constant speed down the hill.
State the magnitude and direction of the resistive force acting on the car.
magnitude of resistive force
N
direction of resistive force
(2 marks)
b The car reaches the end of the slope and moves onto a horizontal road at
point A on Figure 6. The speed of the car at point A is 18 m s–1. Assume that
the resistive force does not change from its value in part a ii.
Calculate the time that elapses, after passing point A, before the car stops.
Time taken to stop
s (4 marks)
From AQA Physics B PHYB2 Physics Keeps Us Going June 2010 (Question 10)
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7