A person trying to lose weight (dieter) lifts a 10 kg mass, one thousand times, to a height of 0.5 m each time. Assume that the potential energy lost each time she lowers the mass is dissipated. (a) How much work does she do against the gravitational force ?

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

Answer carefully, with reasons :
(b) Is the total linear momentum conserved during the short time of an elastic collision of two balls ?

State if each of the following statements is true or false. Give reasons for your answer.
(a) In an elastic collision of two bodies, the momentum and energy of each body is conserved.

The blades of a windmill sweep out a circle of area $A$. (c) Assume that the windmill converts 25% of the wind’s energy into electrical energy, and that $A = 30 \text{ m}^2$, $v = 36 \text{ km/h}$ and the density of air is $1.2 \text{ kg m}^{-3}$. What is the electrical power produced ?

The sign of work done by a force on a body is important to understand. State carefully if the following quantities are positive or negative:
(b) work done by gravitational force in the above case,

Answer carefully, with reasons :
(a) In an elastic collision of two billiard balls, is the total kinetic energy conserved during the short time of collision of the balls (i.e. when they are in contact) ?

State if each of the following statements is true or false. Give reasons for your answer.
(b) Total energy of a system is always conserved, no matter what internal and external forces on the body are present.

A body of mass 0.5 kg travels in a straight line with velocity $v = ax^{3/2}$ where $a = 5 \text{ m}^{-1/2} \text{ s}^{-1}$. What is the work done by the net force during its displacement from $x = 0$ to $x = 2$ m ?

Answer the following :
(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 ?

State if each of the following statements is true or false. Give reasons for your answer.
(d) In an inelastic collision, the final kinetic energy is always less than the initial kinetic energy of the system.

The sign of work done by a force on a body is important to understand. State carefully if the following quantities are positive or negative:
(d) work done by an applied force on a body moving on a rough horizontal plane with uniform velocity,

The sign of work done by a force on a body is important to understand. State carefully if the following quantities are positive or negative:
(c) work done by friction on a body sliding down an inclined plane,

Answer the following : (d) In Fig. 6.13(i) the man walks 2 m carrying a mass of 15 kg on his hands. In Fig. 6.13(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 ?

State if each of the following statements is true or false. Give reasons for your answer.
(c) Work done in the motion of a body over a closed loop is zero for every force in nature.

A trolley of mass 300 kg carrying a sandbag of 25 kg is moving uniformly with a speed of 27 km/h on a frictionless track. After a while, sand starts leaking out of a hole on the floor of the trolley at the rate of $0.05 \text{ kg s}^{-1}$. What is the speed of the trolley after the entire sand bag is empty ?

A body is moving unidirectionally under the influence of a source of constant power. Its displacement in time $t$ is proportional to

Underline the correct alternative :
(a) When a conservative force does positive work on a body, the potential energy of the body...

The sign of work done by a force on a body is important to understand. State carefully if the following quantities are positive or negative:
(a) work done by a man in lifting a bucket out of a well by means of a rope tied to the bucket.

A family uses 8 kW of power. (a) Direct solar energy is incident on the horizontal surface at an average rate of 200 W per square meter. If 20% of this energy can be converted to useful electrical energy, how large an area is needed to supply 8 kW?