EIAT Forces, Torque, and Motion 5 — Questions and Answers
Question 1: An elevator safety gear grips the guide rails to stop the car. The stopping force is an example of:
- Gravitational force
- Magnetic force
- Friction force (Correct answer)
- Tension force
Correct answer: Friction force
Safety gear clamps the rail and uses friction to decelerate and stop the car.
Question 2: If a motor's output torque doubles while its rotational speed stays the same, what happens to its output power?
- Power is halved
- Power stays the same
- Power doubles (Correct answer)
- Power quadruples
Correct answer: Power doubles
Power = Torque × angular velocity; doubling torque at constant speed doubles power.
Question 3: A 1,000 kg elevator car is at rest. What is the tension in the supporting rope? (g = 9.8 m/s²)
- 980 N
- 9,800 N (Correct answer)
- 10,000 N
- 98,000 N
Correct answer: 9,800 N
At rest (no acceleration), tension equals weight = 1,000 × 9.8 = 9,800 N.
Question 4: Which condition must be true for an object to be in rotational equilibrium?
- Net force = 0 only
- Net torque = 0 only
- Both net force and net torque = 0 (Correct answer)
- Angular velocity = 0
Correct answer: Both net force and net torque = 0
Complete mechanical equilibrium requires both zero net force (translational) and zero net torque (rotational).
Question 5: An elevator travels from floor 1 to floor 10, accelerates for 2 s, travels at constant speed for 8 s, then decelerates for 2 s. During which phase is the rope tension greatest?
- Constant speed phase
- Deceleration phase
- Acceleration phase (Correct answer)
- Tension is equal in all phases
Correct answer: Acceleration phase
During upward acceleration, the rope must support the car's weight plus provide the net upward force, making tension greatest.
Question 6: A hydraulic elevator piston has an area of 0.05 m² and supports a load requiring 50,000 N. What fluid pressure is needed?
- 250 Pa
- 2,500 Pa
- 25,000 Pa
- 1,000,000 Pa (Correct answer)
Correct answer: 1,000,000 Pa
Pressure = Force / Area = 50,000 / 0.05 = 1,000,000 Pa (1 MPa).
Question 7: When a rotating drum's radius is doubled while keeping torque constant, what happens to the rope tension it can produce?
- Tension doubles
- Tension is halved (Correct answer)
- Tension is unchanged
- Tension quadruples
Correct answer: Tension is halved
Tension = Torque / radius; doubling radius with constant torque halves the tension.
EIAT Forces, Torque, and Motion 5
An elevator safety gear grips the guide rails to stop the car.
The stopping force is an example of: