Physics Mechanics 3 — Questions and Answers
Question 1: A 2 kg object moving at 6 m/s has its velocity reduced to 2 m/s by friction. How much kinetic energy was lost?
- 32 J (Correct answer)
- 16 J
- 4 J
- 36 J
Correct answer: 32 J
ΔKE = ½(2)(6²) − ½(2)(2²) = 36 − 4 = 32 J.
Question 2: According to Newton's Third Law, when a horse pulls a cart forward, the cart pulls the horse:
- Forward with a smaller force
- Backward with an equal and opposite force (Correct answer)
- Backward with a smaller force
- Not at all
Correct answer: Backward with an equal and opposite force
Newton's Third Law states that every action force has an equal and opposite reaction force, so the cart pulls the horse backward with the same magnitude.
Question 3: A spring with a spring constant of 200 N/m is compressed by 0.1 m. How much elastic potential energy is stored?
- 1 J (Correct answer)
- 2 J
- 20 J
- 0.1 J
Correct answer: 1 J
Elastic PE = ½kx² = ½ × 200 × (0.1)² = 1 J.
Question 4: Which condition must be true for an object to be in static equilibrium?
- Net force is zero and net torque is zero (Correct answer)
- Net force is zero only
- Net torque is zero only
- The object must be at rest and have no acceleration
Correct answer: Net force is zero and net torque is zero
Static equilibrium requires both the net force and the net torque on the object to equal zero.
Question 5: An elevator accelerates upward at 2 m/s². What does a 70 kg person feel as their apparent weight? (g = 9.8 m/s²)
- 826 N (Correct answer)
- 686 N
- 140 N
- 546 N
Correct answer: 826 N
Apparent weight = m(g + a) = 70 × (9.8 + 2) = 70 × 11.8 = 826 N.
Question 6: A wheel rotating at 120 rpm is brought to rest in 4 seconds. What is its angular deceleration in rad/s²?
- π rad/s² (Correct answer)
- 30π rad/s²
- 2π rad/s²
- 60 rad/s²
Correct answer: π rad/s²
120 rpm = 4π rad/s; α = Δω/t = 4π/4 = π rad/s².
Question 7: Which of the following correctly describes the center of mass of a system of particles?
- The point where all mass is physically concentrated
- The average position of mass weighted by each particle's mass (Correct answer)
- The geometric center of the object
- The point of maximum density
Correct answer: The average position of mass weighted by each particle's mass
The center of mass is the mass-weighted average position of all particles in the system.
Physics Mechanics 3
A 2 kg object moving at 6 m/s has its velocity reduced to 2 m/s by friction.
How much kinetic energy was lost?