Newton's first law is also called the law of inertia and force is measured in newtons, so this Class 9 sheet opens with the name and the unit behind motion. Momentum is recorded as mass × velocity, and force pairs act on two different bodies.
Key Takeaways
Newton's first law is the law of inertia (Q1).
The SI unit of force is the newton (Q2).
Momentum is mass × velocity (Q5).
Section A: Multiple Choice Questions (1 Mark Each)
Choose the correct option for each question.
1.Newton's first law of motion is also called the law of
(a) gravitation(b) inertia(c) conservation of momentum(d) friction
2.What is the SI unit of force?
(a) newton(b) joule(c) pascal(d) watt
3.The relation F = ma represents Newton's
(a) first law of motion(b) second law of motion(c) third law of motion(d) law of gravitation
4.Action and reaction forces
(a) act on the same body(b) act on two different bodies(c) always cancel each other(d) act in the same direction
5.The momentum of a body is defined as
(a) mass × acceleration(b) mass × velocity(c) force × time(d) velocity ÷ mass
6.Which of the following has the greatest inertia?
(a) a bicycle(b) a motorcycle(c) a car(d) a loaded truck
Section B: Short Answer Type Questions (2 Marks Each)
Show all steps clearly.
7.State Newton's first law of motion.
8.Define momentum and state its SI unit.
9.State Newton's second law of motion in terms of the rate of change of momentum.
10.Why is it easier to stop a tennis ball than a cricket ball moving with the same speed?
11.State the law of conservation of momentum.
12.Explain why a person falls backward when a bus suddenly starts moving forward.
13.Why does a gun recoil when a bullet is fired from it?
14.What is the difference between balanced and unbalanced forces?
Section C: Numericals & Word Problems (3 Marks Each)
Apply the concepts to solve the problems. Show all working.
15.A force of 10 N acts on a body of mass 2 kg. Find the acceleration produced. (F = ma)
16.A body of mass 5 kg is moving with a velocity of 10 m/s. Find its momentum. (p = mv)
17.A ball of mass 0.5 kg moving at 20 m/s is stopped by a fielder in 0.1 s. Find the average force applied by the fielder. (Force = change in momentum ÷ time)
18.A car of mass 1000 kg moving at 20 m/s is brought to rest by the brakes in 5 s. Find the retarding force applied by the brakes. (F = m × (v - u) ÷ t)
19.A body of mass 2 kg has a momentum of 10 kg m/s. Find its velocity. (v = p ÷ m)
20.A bullet of mass 20 g is fired at a speed of 100 m/s and is stopped by a wooden block in 0.01 s. Find the average force exerted by the block. (Force = change in momentum ÷ time)
Answer Key
1. b) inertia
2. a) newton
3. b) second law of motion
4. b) act on two different bodies
5. b) mass × velocity
6. d) a loaded truck
7. Refer to solution guide.
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End of Worksheet
People Also Ask
What is Newton's first law also called?
The law of inertia, option (b) in this worksheet (Q1).
What is the SI unit of force?
The newton, option (a) in this worksheet (Q2).
What is momentum equal to?
Mass × velocity, option (b) in this worksheet (Q5).
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