NCERT Exemplar solutions for Science [English] Class 9 chapter 9 - Force and Laws of Motion [Latest edition]

Which of the following statement is not correct for an object moving along a straight path in an accelerated motion?

According to the third law of motion, action and reaction

A goalkeeper in a game of football pulls his hands backwards after holding the ball shot at the goal. This enables the goalkeeper to

The inertia of an object tends to cause an object :

A passenger in a moving train tosses a coin which falls behind him. This shows that the motion of train is :

An object of mass 2 kg is sliding with a constant velocity of 4 m/s on a frictionless horizontal table. The force required to keep this object moving with the same velocity is :

Rocket works on the principle of conservation of

A water tanker filled up to `2/3` of its tank with water is running at a uniform speed. When the brakes are suddenly applied, the water in its tank would 

There are three solids made up of aluminium, steel and wood, of the same shape and same volume. Which of them would have the highest inertia?

Two balls of the same size but of different materials, rubber and iron are kept on the smooth floor of a moving train. The brakes are applied suddenly to stop the train. Will the balls start rolling? If so, in which direction? Will they move at the same speed? Give reasons for your answer.

Two identical bullets are fired one by a light rifle and another by a heavy rifle with the same force. Which rifle will hurt the shoulder more and why?

A horse continues to apply force in order to move a cart with a constant speed. Explain why?

Suppose a ball of mass m is thrown vertically upward with an initial speed v, its speed decreases continuously till it becomes zero. Thereafter, the ball begins to fall downward and attains the speed v again before striking the ground. It implies that the magnitude of the initial and final momentums of the ball are the same. Yet, it is not an example of conservation of momentum. Explain why?

Velocity versus time graph of a ball of mass 50 g rolling on a concrete floor is shown in Fig. 9.1. Calculate the acceleration and frictional force of the floor on the ball.

A truck of mass M is moved under a force F. If the truck is then loaded with an object equal to the mass of the truck and the driving force is halved, then how does the acceleration change?

Two friends on roller-skates are standing 5 m apart facing each other. One of them throws a ball of 2 kg towards the other, who catches it, How will this activity affect the position of the two? Explain your answer.

The water sprinkler used for grass lawns begins to rotate as soon as the water is supplied. Explain the principle on which it works.

Using the second law of motion, derive the relation between force and acceleration. A bullet of 10 g strikes a sand-bag at a speed of 103 m s-1 and gets embedded after travelling 5 cm. Calculate

(i) the resistive force exerted by the sand on the bullet

(ii) the time is taken by the bullet to come to rest.

Derive the unit of force using the second law of motion. A force of 5N produces an acceleration of 8 m s^–2 on a mass m₁ and an acceleration of 24 m s^–2 on a mass m₂. What acceleration would the same force provide if both the masses are tied together?

What is momentum? Write its SI unit. Interpret force in terms of momentum. Represent the following graphically

(a) momentum versus velocity when mass is fixed.

(b) momentum versus mass when velocity is constant.