WTMA Force, Motion, and Friction 3 — Questions and Answers
Question 1: A 5 kg object accelerates at 4 m/s². What is the net force acting on it?
- 20 N (Correct answer)
- 1.25 N
- 9 N
- 45 N
Correct answer: 20 N
Using Newton's second law: F = ma = 5 kg × 4 m/s² = 20 N.
Question 2: Two workers push a crate from opposite sides with equal force. What is the result?
- The crate does not move (Correct answer)
- The crate accelerates toward the stronger worker
- The crate spins in place
- Friction increases dramatically
Correct answer: The crate does not move
Equal and opposite forces produce a net force of zero, so the crate remains stationary (assuming it was at rest).
Question 3: A sled slides down a snowy hill and reaches the flat ground. What eventually stops it on the flat?
- Friction between sled runners and snow (Correct answer)
- Gravity reversing direction
- Normal force increasing
- Momentum running out naturally
Correct answer: Friction between sled runners and snow
Friction between the sled runners and the snow acts opposite to the direction of motion, gradually decelerating the sled to a stop.
Question 4: Which scenario shows Newton's third law of motion in action?
- A rocket expels gas downward and rises upward (Correct answer)
- A ball rolling downhill accelerates
- A car braking to a stop
- A box resting on a table
Correct answer: A rocket expels gas downward and rises upward
A rocket demonstrates Newton's third law: the action of expelling gas downward produces an equal and opposite reaction force upward.
Question 5: A wrench handle is extended by adding a longer handle. How does this affect the force needed to turn a bolt?
- Less force is needed (Correct answer)
- More force is needed
- The same force is needed
- Force is no longer relevant
Correct answer: Less force is needed
A longer handle increases the moment arm (torque), allowing the same bolt to be turned with less applied force.
Question 6: An ice skater pushes off a wall and glides backward. Which law explains this motion?
- Newton's third law (Correct answer)
- Newton's first law
- Law of conservation of energy
- Archimedes' principle
Correct answer: Newton's third law
Newton's third law: the skater pushes the wall (action) and the wall pushes the skater backward with an equal and opposite force (reaction).
Question 7: A block is on a ramp inclined at 30°. Which component of gravity acts parallel to the ramp surface and pulls the block downhill?
- mg sin(30°) (Correct answer)
- mg cos(30°)
- mg tan(30°)
- mg alone
Correct answer: mg sin(30°)
The component of gravitational force parallel to an inclined surface is mg sin(θ), where θ is the angle of inclination.
WTMA Force, Motion, and Friction 3
A 5 kg object accelerates at 4 m/s².
What is the net force acting on it?