How much work is done by mass M moving once around a horizontal circle of radius r?

Friction is a non-conservative force. Why?

If the momentum and total energy is conserved, then define the collision is occurred?

Which physical terms remain conserved in an inelastic collision?

What is the loss in kinetic energy after collision, if the target body is initially at rest?

A spring is cut into two equal halves. How is the spring constant of each half affected?

What happen when two identical objects moving mutually opposite directions suffer elastic collision?

 Is work done a scalar or a vector?

In a game of tug of war , one team is slowly giving way to the other.Which team is doing positive work and which team nagative?

A molecule in a gas container hits a horizontal wall with speed 200 m s^–1 and angle 30° with the normal, and rebounds with the same speed. Is momentum conserved in the collision ? Is the collision elastic or inelastic ?

A bolt of mass 0.3 kg falls from the ceiling of an elevator moving down with a uniform speed of 7ms^-1 .It hits the floor of the elevator (length of the elevator = 3m) and does not rebound. What is the heat produced by the impact? Would your answer be different if the elevator were stationary?

A body constrained to move along the z-axis of a coordinate system is subject to a constant force F given by F =\((-\hat{i}+\hat{2j}+\hat{3k})\) N, Where \(\hat{i}\), \( \hat{j} \)and \(\hat{k}\) are unit vectors along the x-, y- and z-axis of the system respectively. What is the work done by this force in moving the body a distance of 4 m along the z-axis ?

The bob A of a pendulum released from 30° to the vertical hits another bob B of the same mass at rest on a table as shown in figure.

How high does the bob A rise after the collision? Neglect the size of the bobs and assume the collision to be elastic.

A pump on the ground floor of a building can pump up water to fill a tank of volume 30 m³ in 15 min. If the tank is 40 m above the ground, and the efficiency of the pump is 30%, how much electric power is consumed by the pump ?

What is the amount of work done by  (i) a weight  - lifter in holding a weight of 120 kg on his shoulder for 30 s? 
(ii) a locomotive against gravity , if it is travelling on a level plane?

A rain drop of radius 2 mm falls from a height of 500 m above the ground. It falls with decreasing acceleration (due to viscous resistance of the air) until at half its original height, it attains its maximum (terminal) speed, and moves with uniform speed thereafter. What is the work done by the gravitational force on the drop in the first and second half of its journey ? What is the work done by the resistive force in the entire journey if its speed on reaching the ground is 10 m s^–1 ?

Abody of mass of 2 kg initially at rest moves under the action of an applied horizontally force of 7 N on a table with coefficient of kinetic friction =0.1. Compute the
(i) work done by the applied force in 10 s,
(ii) work done by friction in 10 s,
(iii) work done by the net force on the body in 10 s,

Mohan was always jealous of Ravi as Ravi was bette In studies for which everybody praised him.One day, Mohan challenged Ravi to defeat t~In in the race-uphill. They were both good runners but running uphill was difficult. Mohan ran very fast and was ahead of Ravi. After sometime, Mohan became breathless and started coughing. Ravi who was following him saw his condition and went to help him forgetting their challenge. Then, Mohan realised why everyone praised Ravi and they became
friends forever.
(i) What values of Ravi do you appreciate?
(ii) If the mass of bag is 0.3 kg and is taken up on an inclined plane of length 10 m and height 5 m, then allowed to slide down to bottom. The coefficient of friction between the body and plane is 0.15, what is the; (a) work doneby gravitational force over the round trip? (b) work done by applied force on upward journey?
(iii) What do you mean by positive work and negative work?

A particle of mass moving with an initial velocity u collides inelastically with a particle of mass M initially at rest. if the collision is completely inelastic, then find expressions for 
final velocity of combined entity and

Answer the following :
(a) The casing of a rocket in flight burns up due to friction. At whose expense is the heat energy required for burning obtained? The rocket or the atmosphere?
(b) Comets move around the sun in highly elliptical orbits. The gravitational force on the comet due to the sun is not normal to the comet’s velocity in general. Yet the work done by the gravitational force over every complete orbit of the comet is zero. Why
(c) An artificial satellite orbiting the earth in very thin atmosphere loses its energy gradually due to dissipation against atmospheric resistance, however small. Why then does its speed increase progressively as it comes closer and closer to the earth ?
(d) In Fig. 5.(i) the man walks 2 m carrying a mass of 15 kg on his hands. In Fig. (ii), he walks the same distance pulling the rope behind him. The rope goes over a pulley, and a mass of 15 kg hangs at its other end. In which case is the work done greater ?