BMST Newton's Laws of Motion 3 ā Questions and Answers
Question 1: A 5 kg object accelerates at 4 m/sĀ². What net force is acting on it?
- 1.25 N
- 9 N
- 20 N (Correct answer)
- 0.8 N
Correct answer: 20 N
F = ma = 5 kg Ć 4 m/sĀ² = 20 N.
Question 2: Friction is a force that opposes motion. In terms of Newton's laws, friction affects an object by:
- Increasing its mass
- Reducing the net force and thus acceleration (Correct answer)
- Eliminating inertia
- Creating an equal and opposite velocity
Correct answer: Reducing the net force and thus acceleration
Friction acts opposite to motion, reducing net force, which by F = ma reduces acceleration.
Question 3: A ball rolling on a frictionless surface will:
- Gradually slow down and stop
- Speed up continuously
- Continue rolling at constant speed indefinitely (Correct answer)
- Immediately stop
Correct answer: Continue rolling at constant speed indefinitely
With no friction (no net force), Newton's First Law says the ball maintains constant velocity.
Question 4: When you press your hand against a wall, the wall presses back on your hand. This is an example of:
- Newton's First Law
- Inertia
- Newton's Third Law (Correct answer)
- Newton's Second Law
Correct answer: Newton's Third Law
Newton's Third Law: every action force has an equal and opposite reaction force.
Question 5: Which scenario best demonstrates Newton's Second Law?
- A parked car stays parked
- A heavier cart accelerates less than a lighter one under the same force (Correct answer)
- A swimmer pushing off a wall moves forward
- A book sitting on a desk
Correct answer: A heavier cart accelerates less than a lighter one under the same force
F = ma shows that with equal force, greater mass produces less acceleration.
Question 6: A net force of 0 N acts on a moving object. The object will:
- Decelerate to a stop
- Accelerate
- Continue at constant velocity (Correct answer)
- Change direction
Correct answer: Continue at constant velocity
Zero net force means zero acceleration; the object maintains its current velocity (Newton's First Law).
Question 7: A horse pulls a cart forward. The cart pulls the horse backward with equal force. Why does the system move forward?
- The horse's force is stronger than the cart's force
- The action-reaction forces act on different objects, so net forces on each object differ (Correct answer)
- Newton's Third Law does not apply here
- The ground pushes the cart forward
Correct answer: The action-reaction forces act on different objects, so net forces on each object differ
Action-reaction forces act on different objects; the horse moves forward because the ground's friction on its hooves exceeds the cart's pull.
BMST Newton's Laws of Motion 3
A 5 kg object accelerates at 4 m/sĀ².
What net force is acting on it?