Newton's laws, momentum, impulse, conservationPractice Questions & MCQs

Q1. Why does a heavy lorry require a more powerful engine than a small car to attain the same acceleration?

• A.Because F = m a, more mass needs more force for the same acceleration
• B.Because the lorry has more inertia of motion than the car
• C.Because friction on lorries is less than on cars
• D.Because heavy bodies fall faster than light bodies

Answer: A. Because F = m a, more mass needs more force for the same acceleration

What does the chapter say about this? Newton's second law states the same acceleration of a heavier mass requires a proportionally larger applied force. A more powerful engine can deliver this larger force, and at any given speed, more power. Pick: A) Because F = m a, more mass needs more force for the same acceleration.

Q2. An apple of mass 100 g rests on a table. By Newton's third law, the apple exerts what force on the Earth and in what direction (g = 10 m/s^2)?

• A.1 N directed upward (away from the surface of the Earth, i.e. toward the apple)
• B.10 N upward
• C.1 N downward
• D.0.1 N upward

Answer: A. 1 N directed upward (away from the surface of the Earth, i.e. toward the apple)

Given 100 g, 10 m, asked for the unknown. By The Earth attracts the apple with weight mg = 0.1 × 10 = 1 N (downward). The Earth attracts the apple with weight mg = 0.1 × 10 = 1 N (downward). By Newton's third law, the apple attracts the Earth with 1 N in the opposite direction, i.e. Putting it together option A) 1 N directed upward (away from the surface of the Earth, i.e. toward the apple).

Q3. Why is it easier to stop a moving cricket ball than a moving bullet, even if both have the same speed?

• A.Bullet has greater mass and hence greater momentum than the ball... [actually bullet has LESS mass; correct reason below]
• B.Bullet has much higher velocity than a typical cricket ball, hence greater momentum despite low mass
• C.Bullet, though lighter, often moves much faster; for equal speeds the cricket ball (heavier) actually has more momentum and is harder to stop
• D.Stopping force depends only on mass, not on momentum

Answer: C. Bullet, though lighter, often moves much faster; for equal speeds the cricket ball (heavier) actually has more momentum and is harder to stop

NCERT fact (physics, chapter 'Force and Laws of Motion'): Stopping force depends on the rate of change of momentum. A cricket ball (≈160 g) is much heavier than a bullet (≈10 g). At equal speeds, the cricket ball has 16× the momentum and is in fact harder to stop. The common 'bullet is hard to stop' impression comes from the bullet's much higher speed in real life, which compensates and exceeds the mass difference. Final answer - C) Bullet, though lighter, often moves much faster; for equal speeds the cricket ball (heavier) actually has more momentum and is harder to stop.