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A boy is moving on a straight road against a frictional force of 5 N. After travelling a distance of 1.5 km he forgot the correct path at a round about (Fig.) of radius 100 m. However, he moves on the circular path for one and half cycle and then he moves forward upto 2.0 km. Calculate the work done by him.

Answer: Total distance travelled by the boy = 1500 m + 200 m + (1.5 x 2 πr) Total distance travelled by the boy = 1500 m + 200 m + (1.5... View Article

Avinash can run with a speed of 8 m s^-1 against the frictional force of 10 N, and Kapil can move with a speed of 3 m s^-1 against the frictional force of 25 N. Who is more powerful and why?

Answer: We know, Power = Force × velocity P = F × v Power deliver by Avinash P = 10 × 8 P = 80W Power deliver by Kapil P = 25... View Article

A rocket is moving up with a velocity v. If the velocity of this rocket is suddenly tripled, what will be the ratio of two kinetic energies?

Answer: Let the mass of the rocket = m The kinetic energy of rocket when it moves with velocity v Initial velocity = v K.E = 1/2 mv2 When the... View Article

A body is falling from a height h. After it has fallen from a height h2, it will possess (a) only potential energy (b) only kinetic energy (c) half potential and half kinetic energy (d) more kinetic and less potential energy

Answer: (c) half potential and half kinetic energy When the body is at height h, its potential will be a hundred per cent and kinetic energy will... View Article

Water stored in a dam possesses (a) no energy (b) electrical energy (c) kinetic energy (d) potential energy

Answer:(d) potential energy Potential energy is the energy stored in an object because of its position. Water in the dam possesses energy because... View Article

The work done on an object does not depend upon the (a) displacement (b) force applied (c) angle between force and displacement (d) initial velocity of the object

Answer:(d) the initial velocity of the object Work done is the product of force and displacement hence force and displacement are the required... View Article

A girl is carrying a school bag of 3 kg mass on her back and moves 200 m on a levelled road. The work done against the gravitational force will be (g =10 m s^-2) (a) 6 ×10³ J (b) 6 J (c) 0.6 J (d) zero

Answer: (d) zero Here Direction of work done is perpendicular to the gravitational force direction. Hence the work done against gravity is zero.... View Article

An iron sphere of mass 10 kg has the same diameter as an aluminium sphere of mass is 3.5 kg. Both spheres are dropped simultaneously from a tower. When they are 10 m above the ground, they have the same (a) acceleration (b) momenta (c) potential energy (d) kinetic energy

Answer: The masses of the iron and aluminium spheres are different. Both will, however, fall under the acceleration due to gravity g=9.8m/s2.... View Article

In case of negative work the angle between the force and displacement is (a) 0° (b) 45° (c) 90° (d ) 180°

Answer: (d) 1800 The amount of work done can be positive, negative, or zero. The force of gravity acts in the downward direction when a body is... View Article

A car is accelerated on a levelled road and attains a velocity 4 times of its initial velocity. In this process the potential energy of the car (a) does not change (b) becomes twice to that of initial (c) becomes 4 times that of initial (d) becomes 16 times that of initial

Answer: (a) does not change Potential energy is the product of height, mass and gravity. Hence height is a factor in determining potential... View Article

When a body falls freely towards the earth, then its total energy (a) increases (b) decreases (c) remains constant (d) first increases and then decreases

Answer: (c) remains constant Because a system's total energy is always conserved, as a body falls freely towards the earth, its total energy... View Article

A ball weighing 4 kg of density 4000 kg m–3 is completely immersed in water of density 103 kg m–3 Find the force of buoyancy on it. (Given g = 10 m s–2)

Answer: The magnitude of the buoyant force given by F = Vpg where p = Density of water V = volume of water displaced by the body g = The gravity... View Article

A cube of side 5 cm is immersed in water and then in saturated salt solution. In which case will it experience a greater buoyant force. If each side of the cube is reduced to 4 cm and then immersed in water, what will be the effect on the buoyant force experienced by the cube as compared to the first case for water. Give reason for each case.

Answer: Buoyant force, F = Vpg p = Density of water V = volume of water displaced by the body g = The gravity The volume and density of an... View Article

Two objects of masses m1 and m2 having the same size are dropped simultaneously from heights h1 and h2 respectively. Find out the ratio of time they would take in reaching the ground. Will this ratio remain the same if (i) one of the objects is hollow and the other one is solid and (ii) both of them are hollow, size remaining the same in each case. Give reason.

Answer: Gravitational acceleration of the objects will not depend on their mass or size and hence it will remain the same for all the objects.... View Article

How does the force of attraction between the two bodies depend upon their masses and distance between them? A student thought that two bricks tied together would fall faster than a single one under the action of gravity. Do you agree with his hypothesis or not? Comment.

Answer: The hypothesis is incorrect. Force of attraction between two masses separated by distance r is given by Newton law of gravitation where... View Article

How does the weight of an object vary with respect to mass and radius of the earth. In a hypothetical case, if the diameter of the earth becomes half of its present value and its mass becomes four times of its present value, then how would the weight of any object on the surface of the earth be affected?

Answer: Let M = Mass of the earth R = Radius of the earth Then Weight of the object = M/R2 Original weight W0 = mg = mg M/R2 Hypothetically 4m... View Article

The earth is acted upon by gravitation of Sun, even though it does not fall into the Sun. Why?

Answer: Earth does not fall into the Sun because it continues to revolve around it. A centripetal force is created, which pulls the earth away... View Article

Calculate the average density of the earth in terms of g, G and R.

Answer: g = GM/R2 M = gR2/G Density of earth D= Mass/Volume D = (G× r2)/(G × Ve) Where Ve is the volume of the earth. D =... View Article

The weight of any person on the moon is about 1/6 times that on the earth. He can lift a mass of 15 kg on the earth. What will be the maximum mass, which can be lifted by the same force applied by the person on the moon?

Answer: Weight of person on moon = 1/6th of weight on earth g on moon = 1/6th g on earth The force that is applied by the man to lift mass... View Article

Identical packets are dropped from two aeroplanes, one above the equator and the other above the north pole, both at height h. Assuming all conditions are identical, will those packets take same time to reach the surface of earth. Justify your answer.

Answer: At the poles, acceleration due to gravity is greater than at the equator. As a result, a packet dropped at the north pole from a height... View Article

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