EIAT - Elevator Industry Aptitude Forces, Torque, and Motion Questions and Answers — Questions and Answers
Question 1: An elevator motor needs to generate torque to lift the car. If the radius of the motor's drive sheave is 0.5 meters and the force required to lift the elevator car and its contents is 8,000 Newtons, what is the minimum torque the motor must produce to begin lifting the car, ignoring friction and other losses?
- 2,000 N·m
- 16,000 N·m
- 8,000 N·m
- 4,000 N·m (Correct answer)
Correct answer: 4,000 N·m
Torque is calculated as the product of the force and the radius (lever arm) at which the force is applied (Torque = Force × Radius). In this scenario, the force is 8,000 N and the radius of the sheave is 0.5 m. Therefore, the torque required is 8,000 N × 0.5 m = 4,000 N·m.
Question 2: A technician is inside an elevator that is accelerating upwards at a constant rate. How does the normal force exerted by the elevator floor on the technician compare to the technician's actual weight (the force of gravity)?
- The normal force is less than their weight.
- The normal force is equal to their weight.
- The normal force is greater than their weight. (Correct answer)
- The normal force is zero.
Correct answer: The normal force is greater than their weight.
According to Newton's Second Law (F=ma), a net force is required for acceleration. For the technician to accelerate upwards, the upward force (normal force from the floor) must be greater than the downward force (gravity/weight). This net upward force causes the upward acceleration, making the person feel heavier.
Question 3: A technician needs to slide a heavy, stationary piece of equipment across a machine room floor. Which of the following statements about the forces involved is most accurate?
- The force required to keep the equipment sliding is greater than the force required to start it moving.
- Kinetic friction is the force that must be overcome to start the equipment moving.
- The force of static friction and kinetic friction are always equal.
- The force required to start the equipment moving is greater than the force required to keep it sliding. (Correct answer)
Correct answer: The force required to start the equipment moving is greater than the force required to keep it sliding.
The force of static friction, which prevents an object from moving, is generally greater than the force of kinetic (or sliding) friction, which opposes motion once the object is already moving. Therefore, more force is needed to overcome static friction and start the movement than to overcome kinetic friction and maintain the movement.
Question 4: In an elevator system, the motor provides the most torque during which phase of operation?
- During constant speed travel upwards.
- When the elevator is stationary at a floor.
- During initial acceleration from a stop. (Correct answer)
- During constant speed travel downwards.
Correct answer: During initial acceleration from a stop.
The greatest torque is required to overcome inertia—the resistance of the heavy elevator car to changes in its state of motion. This occurs during the initial acceleration from a standstill. Once the car is moving at a constant speed, the torque needed is less because it only has to overcome friction and the net weight difference, not inertia.
Question 5: An elevator car with a mass of 1,200 kg is perfectly balanced by a counterweight of 1,200 kg. Ignoring friction, what is the net force required from the hoisting machine to make the car travel upwards at a constant velocity?
- 11,760 N
- 1,200 N
- 23,520 N
- 0 N (Correct answer)
Correct answer: 0 N
According to Newton's First Law, an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. Since the elevator is moving at a constant velocity (zero acceleration) and the car is perfectly balanced by the counterweight, no net force is required to maintain this motion, assuming no friction. The motor only needs to overcome any system friction.
Question 6: A technician uses a 1-meter long wrench to tighten a bolt, applying a force of 300 N at the very end of the wrench handle. To generate the same amount of torque, what force would be required if the technician could only grip the wrench at the 0.5-meter mark?
- 150 N
- 300 N
- 600 N (Correct answer)
- 1,200 N
Correct answer: 600 N
Torque is calculated as Force × Radius (or lever arm length). The initial torque is 300 N × 1 m = 300 N·m. To achieve the same torque with a shorter lever arm of 0.5 m, the force must be increased. Force = Torque / Radius = 300 N·m / 0.5 m = 600 N. Halving the length of the lever arm requires doubling the force to produce the same torque.
EIAT - Elevator Industry Aptitude Forces, Torque, and Motion Questions and Answers
An elevator motor needs to generate torque to lift the car.
If the radius of the motor's drive sheave is 0.5 meters and the force required to lift the elevator car and its contents is 8,000 Newtons, what is the minimum torque the motor must produce to begin lifting the car, ignoring friction and other losses?