OAR Mechanical Comprehension: Forces Flashcards

A lever has its fulcrum at the center. A 40 N force is applied 2 m from the fulcrum. To balance, what force must be applied 4 m from the fulcrum on the other side?

Answer: 20 N

Torque balance: 40 × 2 = F × 4 → F = 80/4 = 20 N.

Which quantity represents the rotational effect of a force about a pivot point?

Answer: Torque

Torque (τ = F × d) measures a force's tendency to cause rotation about a pivot.

An object moves in a circle at constant speed. The net force on the object is directed:

Answer: Inward toward the center

Centripetal force always points toward the center of the circle to maintain circular motion.

Two workers push a crate in the same direction: one with 250 N and one with 180 N. A friction force of 130 N opposes motion. What is the net force?

Answer: 300 N

Net force = (250 + 180) − 130 = 430 − 130 = 300 N in the direction of motion.

If you double the mass of an object while keeping the net force constant, what happens to its acceleration?

Answer: Halves

From a = F/m, doubling m while holding F constant cuts acceleration in half.

A spring scale reads 80 N when a block hangs at rest. The block is then placed on a frictionless table and pulled horizontally with 80 N. What is the normal force from the table?

Answer: 80 N

The normal force balances gravity (weight = 80 N); the horizontal pull does not affect the vertical normal force.

A 1,000 N crate is dragged up a frictionless ramp inclined at 30°. What force parallel to the ramp is needed to move it at constant speed?

Answer: 500 N

Force needed = mg sin 30° = 1,000 × 0.5 = 500 N (frictionless, constant speed = equilibrium).