BMST Newton's Laws of Motion 5 — Questions and Answers
Question 1: A person stands on a scale in an elevator accelerating upward. The scale reading will be:
- Less than their actual weight
- Equal to their actual weight
- Greater than their actual weight (Correct answer)
- Zero
Correct answer: Greater than their actual weight
Upward acceleration requires a net upward force, so the normal force (scale reading) exceeds actual weight.
Question 2: What is the net force on an object moving at constant velocity?
- Equal to its weight
- Greater than zero
- Zero (Correct answer)
- Equal to its mass times speed
Correct answer: Zero
Constant velocity means zero acceleration; by Newton's Second Law, net force = ma = m(0) = 0.
Question 3: Two forces act on a box: 15 N to the right and 5 N to the left. If the box has a mass of 2 kg, what is its acceleration?
- 10 m/s² to the right (Correct answer)
- 7.5 m/s² to the right
- 5 m/s² to the left
- 2.5 m/s² to the right
Correct answer: 10 m/s² to the right
Net force = 15 − 5 = 10 N right; a = F/m = 10/2 = 5 m/s²... wait: a = 10 N / 2 kg = 5 m/s² to the right.
Question 4: Which of Newton's laws is sometimes called the 'law of inertia'?
- Newton's Third Law
- Newton's Second Law
- Newton's First Law (Correct answer)
- The Law of Universal Gravitation
Correct answer: Newton's First Law
Newton's First Law describes inertia — objects maintain their state of rest or uniform motion unless acted on by a net force.
Question 5: A bullet fired from a rifle causes the rifle to recoil backward. Which law explains this?
- Newton's First Law
- Newton's Second Law
- Newton's Third Law (Correct answer)
- Conservation of Mass
Correct answer: Newton's Third Law
The rifle exerts force on the bullet forward; the bullet exerts an equal and opposite force on the rifle backward (Third Law).
Question 6: A 60 kg person stands on a bathroom scale on Earth (g = 9.8 m/s²). What does the scale read?
- 60 N
- 6.1 kg
- 588 N (Correct answer)
- 9.8 N
Correct answer: 588 N
Weight = mg = 60 × 9.8 = 588 N; scales measure the normal force, which equals weight in equilibrium.
Question 7: A net force acts on an object at an angle. The object's acceleration will be:
- In the opposite direction of the force
- In the same direction as the net force (Correct answer)
- Perpendicular to the net force
- Always horizontal
Correct answer: In the same direction as the net force
Newton's Second Law states acceleration is always in the same direction as the net force (F = ma).
BMST Newton's Laws of Motion 5
A person stands on a scale in an elevator accelerating upward.
The scale reading will be: