Forces, Torque, and Motion Flashcards

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)

Answer: 1,350 N downward

Net force = mass × acceleration = 900 × 1.5 = 1,350 N downward.

What is the mechanical advantage of a pulley system that requires 250 N of effort to lift a 1,000 N load?

Answer: 4

Mechanical advantage = Load / Effort = 1,000 / 250 = 4.

A guide rail exerts a horizontal normal force on an elevator car. This force is best described as:

Answer: A reaction force perpendicular to the rail surface

Normal force is always perpendicular to the contact surface, here the rail face.

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?

Answer: 4 rad/s

ω = v / r = 2 / 0.5 = 4 rad/s.

During free fall, what does a person feel regarding their apparent weight?

Answer: Zero weight (weightlessness)

In free fall, both the person and scale accelerate at g, so the scale reads zero — apparent weightlessness.

A brake applies a friction force of 800 N at a radius of 0.25 m on a drum. What braking torque is produced?

Answer: 200 N·m

Braking torque = Force × radius = 800 × 0.25 = 200 N·m.

Which quantity is conserved when no external torque acts on a rotating system?

Answer: Angular momentum

Angular momentum is conserved in the absence of external torques, analogous to linear momentum without external forces.