Work, Energy and Power

Consider a drop of rain water having mass 1 g falling from a height of 1 km. It hits the ground with a speed of 50 m s-1. Take 'g' constant with a value 10 m s-2. The work done by the (i) gravitational force and the (ii) resistive force of air is

1. (i) 1.25 J (ii) -8.25 J
2. (i) 100 J (ii) 8.75 J
3. (i) 10 J (ii) -8.75 J
4. (i) -10 J (ii) -8.25 J

A body of mass 1 kg begins to move under the action of a time dependent force F = (2t i + 3t2 j) N, where i and j are unit vectors along x and y axis. What power will be developed by the force at the time t?

1. (2t3 + 3t4) W
2. (2t3 + 3t5) W
3. (2t2 + 3t3) W
4. (2t2 + 4t4) W

What is the minimum velocity with which a body of mass m must enter a vertical loop of radius R so that it can complete the loop?

1. 3gR
2. 5gR
3. gR
4. 2gR

Two identical balls A and B having velocities of 0.5 m s-1 and -0.3 m s-1 respectively collide elastically in one dimension. The velocities of B and A after the collision respectively will be :

1. -0.5 m s-1 and 0.3 m s-1
2. 0.5 m s-1 and -0.3 m s-1
3. -0.3 m s-1 and 0.5 m s-1
4. 0.3 m s-1 and 0.5 m s-1

A particle moves from a point (-2 i+5 j ) to (4 j+3 k ) when a force of (4 i+3 j ) N is applied. How much work has been done by the force ?

1. 8 J
2. 11 J
3. 5 J
4. 2 J

A ball is thrown vertically downwards from a height of 20 m with an initial velocity v0. It collides with the ground, loses 50 percent of its energy in collision and rebounds to the same height. The initial velocity v0 is (Take g = 10 m s-2)

1. 28 m s-1
2. 10 m s-1
3. 14 m s-1
4. 20 m s-1

On a frictionless surface, a block of mass M moving at speed v collides elastically with another block of same mass M which is initially at rest. After collision the first block moves at an angle to its initial direction and has a speed v3. The second block's speed after the collision is

1. 3 2v
2. 32v
3. 2 23v
4. 34v

A particle of mass m is driven by a machine that delivers a constant power k watts. If the particle starts from rest the force on the particle at time t is

1. 2mk t-1/2
2. 12 mk t-1/2
3. mk2 t-1/2
4. mk t-1/2

A block of mass 10 kg, moving in x direction with a constant speed of 10 m s-1, is subjected to a retarding force F = 0.1x J/m during its travel from x = 20 m to 30 m. Its final KE will be

1. 275 J
2. 250 J
3. 475 J
4. 450 J

Two particles of masses m1, m2 move with initial velocities u1 and u2. On collision, one of the particles gets excited to higher level, after absorbing energy . If final velocities of particles be v1 and v2 then we must have :

1. 12m1u12 + 12m2u22 - = 12m1v12 + 12m2v22
2. 12m12u12 + 12m22u22 + = 12m12v12 + 12m22v22
3. m12u1 + m22u2 - = m12v1 + m22v2
4. 12m1u12 + 12m2u22 = 12m1v12 + 12m2v22 -