Physics Mechanics 2 — Questions and Answers
Question 1: A 5 kg box slides down a frictionless incline angled at 30° to the horizontal. What is the acceleration of the box?
- 4.9 m/s² (Correct answer)
- 9.8 m/s²
- 8.5 m/s²
- 2.5 m/s²
Correct answer: 4.9 m/s²
Acceleration on a frictionless incline is g·sin(θ) = 9.8 × sin(30°) = 9.8 × 0.5 = 4.9 m/s².
Question 2: A car traveling at 20 m/s applies brakes and decelerates at 4 m/s². How long does it take to stop?
- 5 s (Correct answer)
- 4 s
- 8 s
- 10 s
Correct answer: 5 s
Using v = v₀ + at: 0 = 20 + (−4)t → t = 5 s.
Question 3: Which of the following is a vector quantity?
- Speed
- Mass
- Temperature
- Displacement (Correct answer)
Correct answer: Displacement
Displacement has both magnitude and direction, making it a vector; speed, mass, and temperature are scalars.
Question 4: Two objects of masses 3 kg and 6 kg collide and stick together. If the 3 kg object was moving at 4 m/s and the 6 kg object was at rest, what is their combined velocity after collision?
- 1.33 m/s (Correct answer)
- 2 m/s
- 4 m/s
- 0.67 m/s
Correct answer: 1.33 m/s
By conservation of momentum: (3)(4) = (3+6)v → v = 12/9 ≈ 1.33 m/s.
Question 5: A projectile is launched horizontally from a cliff. Which statement about its motion is correct?
- Horizontal velocity increases due to gravity
- Vertical velocity is constant throughout
- Horizontal and vertical motions are independent (Correct answer)
- The projectile follows a straight-line path
Correct answer: Horizontal and vertical motions are independent
Horizontal and vertical components of projectile motion are independent; gravity affects only the vertical component.
Question 6: What is the net work done on an object that moves in a complete circle at constant speed?
- Equal to the kinetic energy
- Positive
- Negative
- Zero (Correct answer)
Correct answer: Zero
At constant speed there is no change in kinetic energy, so the net work done over any path, including a full circle, is zero.
Question 7: A 10 kg object is raised 3 m vertically. What is the increase in its gravitational potential energy? (g = 9.8 m/s²)
- 294 J (Correct answer)
- 30 J
- 98 J
- 980 J
Correct answer: 294 J
Gravitational PE = mgh = 10 × 9.8 × 3 = 294 J.
Physics Mechanics 2
A 5 kg box slides down a frictionless incline angled at 30° to the horizontal.
What is the acceleration of the box?