1. What is Newton’s First Law also known as?
Answer: Law of Inertia
Explanation: It states that a body remains at rest or in uniform motion unless acted upon by an external force.
2. A 5 kg mass is acted upon by a net force of 20 N. What is its acceleration?
Answer: 4 m/s²
Explanation: ( a = F/m = 20 / 5 = 4 )
3. Action and reaction forces act on the same body. True or False?
Answer: False
Explanation: Action and reaction act on different bodies, simultaneously, and are equal in magnitude but opposite in direction.
4. What is the unit of force in SI?
Answer: Newton (N)
Explanation: 1 Newton = force required to accelerate 1 kg mass by 1 m/s².
5. A body is moving with constant velocity. What is the net external force on it?
Answer: 0
Explanation: Constant velocity → no acceleration → net force = 0 (from Newton’s 2nd law)
6. A force of 10 N acts on a 2 kg mass. Find acceleration.
Answer: 5 m/s²
Explanation: ( a = F/m = 10 / 2 = 5 )
7. What is the direction of frictional force?
Answer: Opposite to the direction of motion
Explanation: Friction always resists relative motion between surfaces.
8. A block of 10 kg is at rest on a table. What is the normal force acting on it? (Take g = 9.8 m/s²)
Answer: 98 N
Explanation: Normal force = weight = mg = 10 × 9.8
9. If a body is in equilibrium, what can you say about the net force?
Answer: Zero
Explanation: Equilibrium implies no acceleration → net external force = 0
10. A body is moving in a circular path with constant speed. Is it in equilibrium?
Answer: No
Explanation: Although speed is constant, direction is changing → acceleration exists → net force ≠ 0
11. A 50 kg person stands in an elevator accelerating upwards at 2 m/s². What is the apparent weight?
Answer: 590 N
Explanation: Apparent weight = m(g + a) = 50(9.8 + 2) = 50 × 11.8 = 590
12. State Newton’s 2nd Law.
Answer: Force = mass × acceleration
Explanation: It gives the relation between force and change in motion (F = ma)
13. A horizontal force of 30 N is applied on a 6 kg block. Find acceleration (neglect friction).
Answer: 5 m/s²
Explanation: a = F/m = 30 / 6 = 5
14. Define inertia.
Answer: Tendency of a body to resist change in its state of motion
Explanation: More mass → more inertia
15. What causes a passenger to jerk forward when a moving bus stops suddenly?
Answer: Inertia
Explanation: Body tends to maintain its motion even when the bus stops.
16. If action = +10 N, what is reaction?
Answer: –10 N
Explanation: Newton’s 3rd Law → reaction is equal in magnitude and opposite in direction.
17. Two blocks of 2 kg and 3 kg are tied together and pulled by 10 N. What is the acceleration of the system?
Answer: 2 m/s²
Explanation: Total mass = 5 kg → a = F/m = 10/5 = 2
18. Can an object move under the action of balanced forces?
Answer: Yes
Explanation: If it was already in motion, it will continue moving uniformly (Newton’s 1st Law).
19. What is limiting friction?
Answer: Maximum static friction before motion begins
Explanation: It’s the highest value of static friction just before slipping starts.
20. A man pulls a cart with force 50 N at 60° to horizontal. What is the horizontal component?
Answer: 25 N
Explanation: Horizontal component = F cos θ = 50 × cos(60°) = 50 × 0.5 = 25
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