OAR OAR Mechanical Comprehension: Forces 2 — Questions and Answers
Question 1: A 10 kg box is pushed across a frictionless surface with a net force of 30 N. What is the box's acceleration?
- 0.33 m/s²
- 3 m/s² (Correct answer)
- 300 m/s²
- 20 m/s²
Correct answer: 3 m/s²
Newton's second law: a = F/m = 30/10 = 3 m/s².
Question 2: 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?
- 24 N to the right
- 6 N to the left
- 6 N to the right (Correct answer)
- 24 N to the left
Correct answer: 6 N to the right
Net force = 15 − 9 = 6 N in the direction of the larger force (right).
Question 3: Which of the following best describes a force couple?
- Two equal forces acting in the same direction
- Two equal and opposite forces that produce rotation (Correct answer)
- A single force that creates linear motion
- Two forces that cancel each other out with no rotation
Correct 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.
Question 4: An object is in static equilibrium. Which statement must be true?
- The object is moving at constant velocity
- The net force and net torque on it are both zero (Correct answer)
- All individual forces acting on it are zero
- The object has no mass
Correct 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.
Question 5: 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)
- 500 N
- 400 N
- 600 N (Correct answer)
- 1000 N
Correct answer: 600 N
Mass = 50 kg; scale reads N = m(g + a) = 50(10 + 2) = 600 N.
Question 6: 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?
- 500 N
- 200 N
- 80 N (Correct answer)
- 0.4 N
Correct answer: 80 N
Maximum static friction = μs × Normal force = 0.4 × 200 = 80 N.
Question 7: A block rests on a ramp inclined at 30°. Which component of gravity acts parallel to the ramp surface?
- mg cos 30°
- mg tan 30°
- mg sin 30° (Correct answer)
- mg / sin 30°
Correct answer: mg sin 30°
The component of gravity parallel to the incline equals mg sin θ, which drives the block down the slope.
OAR OAR Mechanical Comprehension: Forces 2
A 10 kg box is pushed across a frictionless surface with a net force of 30 N.
What is the box's acceleration?