WTMA Force, Motion, and Friction 2 — Questions and Answers
Question 1: A 10 kg box is pushed across a floor with a force of 50 N while friction exerts 30 N opposing the motion. What is the net force on the box?
- 20 N forward (Correct answer)
- 50 N forward
- 80 N forward
- 30 N backward
Correct answer: 20 N forward
Net force equals applied force minus friction: 50 N − 30 N = 20 N in the direction of motion.
Question 2: Which surface combination would produce the HIGHEST coefficient of friction?
- Rubber on concrete (Correct answer)
- Steel on ice
- Waxed wood on waxed wood
- Ball bearings on steel
Correct answer: Rubber on concrete
Rubber on concrete has a very high coefficient of friction due to the soft, grippy nature of rubber and the rough texture of concrete.
Question 3: A car traveling at 60 mph suddenly brakes. Which force brings the car to a stop?
- Friction between tires and road (Correct answer)
- Air resistance only
- Gravity pulling the car down
- Engine braking force
Correct answer: Friction between tires and road
The friction force between the tires and the road surface is what decelerates the car to a stop.
Question 4: If you double the weight of a box sliding across a floor, what happens to the kinetic friction force?
- It doubles (Correct answer)
- It stays the same
- It halves
- It quadruples
Correct answer: It doubles
Kinetic friction force equals the coefficient of kinetic friction times the normal force, so doubling the weight (and thus normal force) doubles friction.
Question 5: A ball rolls along a flat surface and gradually slows to a stop. Which force is responsible?
- Rolling friction (Correct answer)
- Static friction
- Applied force
- Normal force
Correct answer: Rolling friction
Rolling friction (or rolling resistance) acts against the motion of a rolling object, causing it to decelerate over time.
Question 6: An object is moving at constant velocity on a surface. What must be true about the forces acting on it?
- Net force is zero (Correct answer)
- Applied force exceeds friction
- Friction force is zero
- Gravity is absent
Correct answer: Net force is zero
By Newton's first law, constant velocity means no acceleration, which requires the net force to be zero — applied force equals friction.
Question 7: Which of the following best describes static friction compared to kinetic friction on the same surfaces?
- Static friction is greater than kinetic friction (Correct answer)
- Kinetic friction is greater than static friction
- They are always equal
- Static friction only acts on vertical surfaces
Correct answer: Static friction is greater than kinetic friction
Static friction is generally greater than kinetic friction because it takes more force to start an object moving than to keep it moving.
WTMA Force, Motion, and Friction 2
A 10 kg box is pushed across a floor with a force of 50 N while friction exerts 30 N opposing the motion.
What is the net force on the box?