EIAT Forces, Torque, and Motion 3 — Questions and Answers
Question 1: A 900 kg elevator car accelerates downward at 1.5 m/s². What is the net force acting on it? (g = 9.8 m/s²)
- 900 N downward
- 1,350 N downward (Correct answer)
- 7,470 N downward
- 8,820 N downward
Correct answer: 1,350 N downward
Net force = mass × acceleration = 900 × 1.5 = 1,350 N downward.
Question 2: What is the mechanical advantage of a pulley system that requires 250 N of effort to lift a 1,000 N load?
- 0.25
- 2
- 4 (Correct answer)
- 10
Correct answer: 4
Mechanical advantage = Load / Effort = 1,000 / 250 = 4.
Question 3: A guide rail exerts a horizontal normal force on an elevator car. This force is best described as:
- A frictional force opposing motion
- A gravitational force
- A reaction force perpendicular to the rail surface (Correct answer)
- A tension force along the rail
Correct answer: A reaction force perpendicular to the rail surface
Normal force is always perpendicular to the contact surface, here the rail face.
Question 4: If the rope speed in a traction elevator is 2 m/s and the sheave radius is 0.5 m, what is the sheave's angular velocity?
- 1 rad/s
- 2.5 rad/s
- 4 rad/s (Correct answer)
- 5 rad/s
Correct answer: 4 rad/s
ω = v / r = 2 / 0.5 = 4 rad/s.
Question 5: During free fall, what does a person feel regarding their apparent weight?
- Normal weight
- Doubled weight
- Zero weight (weightlessness) (Correct answer)
- Weight equal to mass only
Correct answer: Zero weight (weightlessness)
In free fall, both the person and scale accelerate at g, so the scale reads zero — apparent weightlessness.
Question 6: A brake applies a friction force of 800 N at a radius of 0.25 m on a drum. What braking torque is produced?
- 200 N·m (Correct answer)
- 400 N·m
- 800 N·m
- 3,200 N·m
Correct answer: 200 N·m
Braking torque = Force × radius = 800 × 0.25 = 200 N·m.
Question 7: Which quantity is conserved when no external torque acts on a rotating system?
- Kinetic energy
- Angular momentum (Correct answer)
- Linear momentum
- Potential energy
Correct answer: Angular momentum
Angular momentum is conserved in the absence of external torques, analogous to linear momentum without external forces.
EIAT Forces, Torque, and Motion 3
A 900 kg elevator car accelerates downward at 1.5 m/s².
What is the net force acting on it? (g = 9.8 m/s²)