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Which of the following is not a physical change? (a) Boiling of water to give water vapour (b) Melting of ice to give water (c) Dissolution of salt in water (d) Combustion of Liquefied Petroleum Gas (LPG)

Answer: (d) Combustion of Liquefied Petroleum Gas (LPG) Combustion is always a chemical change because a new compound is formed after burning and... View Article

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.

Answer: The quantity of motion of a moving body is called momentum. It is measured as the product of mass and velocity. Momentum = mass ×... View Article

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

Answer: Newton’s 2nd law states that the acceleration of an object as produced by a net force is directly proportional to the magnitude of... View Article

Using 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 and gets embedded after travelling 5 cm. Calculate (i) the resistive force exerted by the sand on the bullet (ii) the time taken by the bullet to come to rest.

Answer: Given m = 10 g = 10/1000 kg u = = 103 m/s v = 0 s = 5 cm = 5/100 m (i) the resistive force exerted by the sand on the bullet By using... View Article

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

Answer: Newton’s third law of motion states that when one body exerts a force on the other body, the first body experiences a force which... View Article

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.

Answer: Distance between them will increase. Before throwing the ball, the momentum of both of them will be zero. To conserve the momentum, the... View Article

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?

Answer: Force = mass x acceleration F = m × a a1 = F/m When mass is doubled force is halved then m = 2m F = F/2 a2 = F/4m a1/a2 =... View Article

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

Answer: Given, m = 50g F =? Force = mass × acceleration F = (50/100) x 10 F = 0.5 N Velocity = 80ms-1 Velocity decelerates due to the... View Article

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 initial and final momentums of the ball are same. Yet, it is not an example of conservation of momentum. Explain why?

Answer: If the external force did not act on the system, the momentum of that system remains constant. In the given case, change in velocity is... View Article

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

Answer: When cart moves on the road it has to encounter friction. In order to keep the cart moving horse should overcome the friction. Hence it... View Article

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?

Answer: The momentum of the bullet depends on the backward momentum of the rifle. As per Newton’s third law of motion: recoil velocity is... View Article

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 with the same speed? Give reasons for your answer.

Answer: Steel Yes, the balls start rolling in the direction of the train’s movement. When brakes are applied, the train will come to rest... View Article

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

Answer: Steel Inertia depends on the mass of the object. For the solids with the same size and volume, inertia is determined by their mass. Hence... View Article

A water tanker filled up to 2/3 of its height is moving with a uniform speed. On sudden application of the brake, the water in the tank would (a) move backward (b) move forward (c) be unaffected (d) rise upwards

Answer: (b) move forward On applying brakes water tanker comes to rest but water will be in motion this makes the water to come forward. When a... View Article

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 the object moving with the same velocity is (a) 32 N (b) 0 N (c) 2 N (d) 8 N

Answer: (b) 0 N Newton’s 1st law states that a body at rest or uniform motion will continue to be at rest or uniform motion until and... View Article

The inertia of an object tends to cause the object (a) to increase its speed (b) to decrease its speed (c) to resist any change in its state of motion (d) to decelerate due to friction

Answer: (c) to resist any change in its state of motion Inertia is the property that resists the state of motion of an object. The object remains... View Article

A goalkeeper in a game of football pulls his hands backwards after holding the ball shot at the goal. This enables the goal keeper to (a) exert larger force on the ball (b) reduce the force exerted by the ball on hands (c) increase the rate of change of momentum (d) decrease the rate of change of momentum

Answer: (b) reduce the force exerted by the ball on hands and (d) decrease the rate of change of momentum After holding the ball, the goalkeeper... View Article

According to the third law of motion, action and reaction (a) always act on the same body (b) always act on different bodies in opposite directions (c) have same magnitude and directions (d) act on either body at normal to each other

Answer: (b) always act on different bodies in opposite directions Newton’s third law of motion states that when one body exerts a force on... View Article

Which of the following statement is not correct for an object moving along a straight path in an accelerated motion? (a) Its speed keeps changing (b) Its velocity always changes (c) It always goes away from the earth (d) A force is always acting on it

Answer: (c) It always goes away from the earth Newton’s third law of motion states that when one body exerts a force on the other body, the... View Article

Draw a curve showing density or pressure variations with respect to distance for a disturbance produced by sound. Mark the position of compression and rarefaction on this curve. Also define wavelengths and time period using this curve.

Answer: The distance between two consecutive compressions or two consecutive rarefactions is called wavelength. The time period of a wave is... View Article

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