A-Level Physics Mechanics 2 — Questions and Answers
Question 1: Two forces of 3 N and 4 N act at right angles to each other. What is the magnitude of the resultant force?
- 5 N (Correct answer)
- 7 N
- 1 N
- 3.5 N
Correct answer: 5 N
Using Pythagoras: R = √(3² + 4²) = √(9 + 16) = √25 = 5 N. This is the classic 3-4-5 right triangle.
Question 2: An object moves in a circle at constant speed. In which direction does the centripetal acceleration act?
- Towards the centre of the circle (Correct answer)
- Away from the centre of the circle
- Tangent to the circle in the direction of motion
- Tangent to the circle opposite to the direction of motion
Correct answer: Towards the centre of the circle
Centripetal acceleration always acts towards the centre of the circular path. It continuously changes the direction of velocity without changing its magnitude, keeping the object moving in a circle.
Question 3: A spring with spring constant k = 200 N/m is compressed by 0.15 m. What is the elastic potential energy stored?
- 2.25 J (Correct answer)
- 30 J
- 15 J
- 4.5 J
Correct answer: 2.25 J
Elastic PE = ½kx² = ½ × 200 × 0.15² = ½ × 200 × 0.0225 = 2.25 J.
Question 4: What is the principle of conservation of momentum?
- The total momentum of a closed system remains constant provided no external resultant force acts (Correct answer)
- Momentum is always conserved regardless of external forces
- Kinetic energy is always conserved in collisions
- The total force in a system is always zero
Correct answer: The total momentum of a closed system remains constant provided no external resultant force acts
The principle states that in a closed system (no external resultant force), total momentum before an event equals total momentum after. This applies to all collisions and explosions.
Question 5: A 0.5 kg ball moving at 6 m/s collides with a stationary 1.5 kg ball. They stick together. What is their velocity after the collision?
- 1.5 m/s (Correct answer)
- 3 m/s
- 2 m/s
- 6 m/s
Correct answer: 1.5 m/s
Using conservation of momentum: (0.5 × 6) + (1.5 × 0) = (0.5 + 1.5) × v. So 3 = 2v, giving v = 1.5 m/s. This is a perfectly inelastic collision.
Question 6: On a velocity-time graph, what does the area under the line represent?
- Displacement (Correct answer)
- Acceleration
- Force
- Speed
Correct answer: Displacement
The area under a velocity-time graph gives the displacement of the object. This is because displacement = velocity × time, which corresponds to the area calculation. Areas below the time axis represent displacement in the negative direction.
A-Level Physics Mechanics 2
Two forces of 3 N and 4 N act at right angles to each other.
What is the magnitude of the resultant force?