OAR Mechanical Comprehension: Forces Flashcards

A 10 kg box is pushed across a frictionless surface with a net force of 30 N. What is the box's acceleration?

Answer: 3 m/s²

Newton's second law: a = F/m = 30/10 = 3 m/s².

Two forces act on an object: 15 N to the right and 9 N to the left. What is the magnitude and direction of the net force?

Answer: 6 N to the right

Net force = 15 − 9 = 6 N in the direction of the larger force (right).

Which of the following best describes a force couple?

Answer: Two equal and opposite forces that produce rotation

A couple consists of two equal, opposite, non-collinear forces that produce pure rotation (torque) with no net linear force.

An object is in static equilibrium. Which statement must be true?

Answer: The net force and net torque on it are both zero

Static equilibrium requires both the sum of all forces and the sum of all torques to equal zero.

A 500 N person stands on a scale in an elevator accelerating upward at 2 m/s². What does the scale read? (g ≈ 10 m/s²)

Answer: 600 N

Mass = 50 kg; scale reads N = m(g + a) = 50(10 + 2) = 600 N.

If the coefficient of static friction between a box and a floor is 0.4 and the box weighs 200 N, what is the maximum static friction force?

Answer: 80 N

Maximum static friction = μs × Normal force = 0.4 × 200 = 80 N.

A block rests on a ramp inclined at 30°. Which component of gravity acts parallel to the ramp surface?

Answer: mg sin 30°

The component of gravity parallel to the incline equals mg sin θ, which drives the block down the slope.