Linear Momentum and the Second Law

Linear Momentum and the Second Law MDCAT MCQs with answers

12 past paper MCQs on Linear Momentum and the Second Law, from the Force and Motion unit of MDCAT Physics. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

Read the notes first Practise the unit as a quiz

1.The product of force and time is equal to: (MDCAT 2020)

  1. angular momentum
  2. force
  3. change in momentum
  4. velocity
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Correct answer: (c) change in momentum

$F\Delta t$ is the impulse, and the impulse equals the change in momentum.

2.The time rate of change of linear momentum of a body is equal to its: (MDCAT 2020)

  1. force
  2. momentum
  3. power
  4. acceleration
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Correct answer: (a) force

Newton's second law in its general form is $F=\Delta p/\Delta t$.

3.If two equal masses are in motion with the same individual speeds, we can conclude that: (MDCAT 2023)

  1. their momenta are the same
  2. their momenta can be different from each other
  3. their kinetic energies are different from each other
  4. their total energies are different
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Correct answer: (b) their momenta can be different from each other

Momentum is a vector, so equal masses at equal speeds in different directions have different momenta.

4.Product of force and time is equal to: (NUMS MDCAT 2025)

  1. Change in displacement
  2. Change in momentum
  3. Change in velocity
  4. Change in acceleration
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Correct answer: (b) Change in momentum

Force times time is impulse, and impulse equals the change in momentum.

5.A 150 kg car has its velocity reduced from 20 m/s to 10 m/s in 3.0 sec. How large was the average retarding force? (SIBA MDCAT 2025)

  1. 500 N
  2. 2500 N
  3. 1500 N
  4. 1000 N
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Correct answer: (a) 500 N

$F=m\Delta v/\Delta t=150\times10/3$, which is $500\,\mathrm{N}$.

6.A ball of mass m strikes a wall and rebounds with the same speed in the opposite direction, taking the initial direction as positive, the change in the momentum of the ball is: (SIBA MDCAT 2025)

  1. 0
  2. mv
  3. -2mv
  4. -mv
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Correct answer: (c) -2mv

The momentum goes from $mv$ to $-mv$, a change of $-2mv$.

7.If you stop your car quickly by wearing seat belts, chance of injury is greatly reduced because seat belt applied: (NUMS MDCAT 2024)

  1. Extra force
  2. Perpendicular force
  3. Opposite force
  4. Zero force
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Correct answer: (c) Opposite force

The belt supplies the backward force that stops the passenger, and it spreads that stop over a longer time.

8.A ball with momentum 8 kg m/s hits a wall and bounces back without losing K.E. Change in momentum is: (NUMS MDCAT 2024)

  1. 4 Ns
  2. -16 Ns
  3. 16 Ns
  4. 8 Ns
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Correct answer: (c) 16 Ns

The momentum goes from $+8$ to $-8$, a change of $16\,\mathrm{N\,s}$.

9.A car and truck is running with same velocity, a constant and same force applied to both, which will stop first: (PMC MDCAT 2022)

  1. Car
  2. Truck
  3. Both at the same time
  4. Information insufficient
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Correct answer: (a) Car

The same force acting for the same change of velocity stops the smaller mass first.

10.A gun fires a bullet of mass 40 g with a velocity of 1200 ms-1 . The man holding it can exert a maximum force of 144 N on the gun. How many bullets can he fire per second at the most? (PMC MDCAT 2022)

  1. 1
  2. 2
  3. 3
  4. 4
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Correct answer: (c) 3

Each shot carries $0.04\times1200=48\,\mathrm{N\,s}$ of momentum, and $144/48$ is three a second.

11.A force of 50 dynes is acted on a body of mass 5g which is at rest for an interval of 3 seconds, then impulse is (PMC MDCAT 2022)

  1. 0.00015 N.s
  2. 0.0015 N.s
  3. 0.15 N.s
  4. 1.6 N.s
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Correct answer: (b) 0.0015 N.s

$50\,\mathrm{dyne}$ is $5\times10^{-4}\,\mathrm{N}$, and over three seconds the impulse is $1.5\times10^{-3}\,\mathrm{N\,s}$.

12.The newton-second is the unit of: (PMC MDCAT 2020)

  1. Work
  2. Power
  3. Impulse
  4. Momentum
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Correct answer: (c) Impulse

Force times time is impulse, measured in newton seconds.

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