Daily Practice Problems

Class 9 Science

Force and Laws of Motion

Class 9 Science

Force and Laws of Motion

**Question 1.**

What is the first law of motion?

**Question 2.**

Define the property of an object ‘inertia’.

**Question 3.**

What do you understand by the term ‘momentum’?

**Question 4.**

What does second law of motion state?

**Question 5.**

Give mathematical formulation of second law of motion.

**Question 6.**

What do you understand by ‘conservation of momentum’?

**Question 7.**

Force of friction always _________ motion of objects.

(a) opposes

(b) follows

(c) both (a) and (b)

(d) none of the above

**Question 8.**

What is the third law motion?

**Question 9.**

How do you define ‘force of one Newton’?

**Question 10.**

A constant force acts on an object of mass 6 kg for a duration of 3 s. It increases the object’s velocity from 4 m-s^{–1} to 8 m-s^{-1}. Find the magnitude of the applied force. Now, if the force was applied for a duration of 4 s, what would be the final velocity of the object?

**Question 11.**

Which would require a greater force- an object accelerating with 1 ms^{-2} having mass 5 kg and an object accelerating with 3 ms^{-2}^{ }having mass 10 kg?

**Question 12.**

A motorcar is moving with a velocity of 90 km/h and it takes 3 s to stop after the brakes are applied. Calculate the force exerted by the brakes on the motorcar if its mass along with the passengers is 1500 kg.

**Question 13.**

A force of 10 N gives a mass m_{1}, an acceleration of 15 m-s^{–2} and a mass m_{2}, an acceleration of 30 m-s^{-2}. What acceleration would it give if both the masses were tied together?

**Question 14.**

A bullet of mass 30 g is horizontally fired with a velocity 200 m-s^{-1} from a pistol of mass 3 kg. What is the recoil velocity of the pistol?

**Question 15.**

A girl of mass 50 kg jumps with a horizontal velocity of 6 m-s^{-1} onto a stationary cart with frictionless wheels. The mass of the cart is 5 kg. What is her velocity as the cart starts moving? Assume that there is no external unbalanced force working in the horizontal direction.

**Question 16.**

A bullet of mass 40 g is horizontally fired with a velocity 500 m-s^{-1} from a pistol of mass 8 kg. What is the recoil velocity of the pistol?

**Question 17.**

Which would require a smaller force- an object accelerating with 3 ms^{-2} having mass 18 kg and an object accelerating with 2 ms^{-2}^{ }having mass 20kg?

**Question 18.**

A force of 20 N gives a mass m_{1}, an acceleration of 12 m-s^{–2} and a mass m_{2}, an acceleration of 40 m-s^{-2}. What acceleration would it give if both the masses were tied together?

**Question 19.**

A bullet of mass 50 g is horizontally fired with a velocity 300 m-s^{-1} from a pistol of mass 5 kg. What is the recoil velocity of the pistol?

**Question 20.**

A boy of mass 35 kg jumps with a horizontal velocity of 5 m-s^{-1} onto a stationary cart with frictionless wheels. The mass of the cart is 6 kg. What is his velocity as the cart starts moving? Assume that there is no external unbalanced force working in the horizontal direction.

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