WTMA Force, Motion, and Friction 4 — Questions and Answers
Question 1: A heavy crate and a light box are pushed with the same force on the same surface. Which accelerates faster?
- The light box (Correct answer)
- The heavy crate
- Both accelerate equally
- Neither accelerates
Correct answer: The light box
From Newton's second law (a = F/m), a smaller mass produces greater acceleration when the same force is applied.
Question 2: Oil is applied to a machine's moving parts. What effect does this have on friction?
- It reduces friction by creating a lubricating film (Correct answer)
- It increases friction to prevent slipping
- It has no effect on friction
- It converts kinetic friction to static friction
Correct answer: It reduces friction by creating a lubricating film
Lubrication separates surfaces with a thin oil film, greatly reducing the coefficient of friction between moving parts.
Question 3: A car goes around a curved road at high speed. What force keeps it on the curved path?
- Friction between tires and road (Correct answer)
- Gravity pulling it inward
- Air resistance pushing it inward
- The car's engine force
Correct answer: Friction between tires and road
Friction between the tires and the road provides the centripetal force needed to keep the car moving in a curved path.
Question 4: Which change would NOT reduce the friction between two sliding surfaces?
- Increasing the contact surface area (Correct answer)
- Adding a lubricant between the surfaces
- Reducing the normal force
- Using smoother materials
Correct answer: Increasing the contact surface area
For most surfaces, friction force is independent of contact area — only the normal force and coefficient of friction matter.
Question 5: A train traveling at constant speed on level track has its engines providing 50,000 N of force. What is the total friction/resistance force?
- 50,000 N (Correct answer)
- 0 N
- More than 50,000 N
- Less than 50,000 N
Correct answer: 50,000 N
At constant velocity, net force is zero, so resistance forces exactly equal the engine's driving force of 50,000 N.
Question 6: When a skydiver reaches terminal velocity, what is true about the forces acting on them?
- Gravity equals air resistance (Correct answer)
- Gravity is greater than air resistance
- Air resistance is greater than gravity
- No forces act on the skydiver
Correct answer: Gravity equals air resistance
Terminal velocity is reached when air resistance (drag) equals gravitational force, resulting in zero net force and constant speed.
Question 7: A block is pushed against a wall with a horizontal force. What prevents the block from sliding down the wall?
- Static friction between block and wall (Correct answer)
- Normal force from the wall
- The block's weight
- Gravity acting horizontally
Correct answer: Static friction between block and wall
The horizontal push creates a normal force against the wall, and static friction acts upward to counterbalance the block's weight.
WTMA Force, Motion, and Friction 4
A heavy crate and a light box are pushed with the same force on the same surface.
Which accelerates faster?