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A freely falling object eventually stops on reaching the ground. What happens to its kinetic energy?

Important Questions on Work and Energy

EASY

Science>Physics>Work and Energy>Energy Transformation

The temperature of the water at the bottom of a water fall is higher than that of the water at the top, because :

EASY

Science>Physics>Work and Energy>Energy Transformation

In any physical or chemical process, the total energy:

EASY

Science>Physics>Work and Energy>Energy Transformation

Describe in your words the law of conservation of energy.

HARD

Science>Physics>Work and Energy>Energy Transformation

A particle is moving in a circle of radius

r

under the action of a force

F = α r^{2}

which is directed towards centre of the circle. Total mechanical energy (kinetic energy + potential energy) of the particle is (take potential energy

= 0

for

r = 0

EASY

Science>Physics>Work and Energy>Energy Transformation

An electric device which converts electric energy into mechanical energy is called

EASY

Science>Physics>Work and Energy>Energy Transformation

A marble P of mass m lies at rest on the edge of a perfectly horizontal surface of a table of height h, as shown in the figure. A second identical marble Q having same mass moving at a speed u strikes it perfectly elastically. The speed acquired by marble P after the collision is (In an elastic collision, momentum as well as kinetic energy are conserved)
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MEDIUM

Science>Physics>Work and Energy>Energy Transformation

Name a machine that converts electrical energy into mechanical energy.

MEDIUM

Science>Physics>Work and Energy>Energy Transformation

If the potential energy between two molecules is given by

U = \frac{A}{r^{6}} - \frac{B}{r^{12}},

then at equilibrium, separation between molecules, and the potential energy are:

EASY

Science>Physics>Work and Energy>Energy Transformation

An electric motor converts:

HARD

Science>Physics>Work and Energy>Energy Transformation

Name the device that converts electrical energy into mechanical energy. Draw its diagram and label the parts.

MEDIUM

Science>Physics>Work and Energy>Energy Transformation

A person trying to lose weight by burning fat lifts a mass of 10 kg upto a height of 1m 1000 times. Assume that the potential energy lost each time he lowers the mass is dissipated. How much fat will he use up considering the work done only when the weight is lifted up? Fat supplies

3.8 \times 10^{7}

J of energy per kg which is converted to mechanical energy with a 20% efficiency rate. Take

g = 9.8 m s^{- 2}

EASY

Science>Physics>Work and Energy>Energy Transformation

State the energy changes in the case of an electric iron while in use.

EASY

Science>Physics>Work and Energy>Energy Transformation

Hydrogen ion and singly ionized helium atom are accelerated, from rest, through the same potential difference. The ratio of final speeds of hydrogen and helium ions is close to:

EASY

Science>Physics>Work and Energy>Energy Transformation

In a simple Pendulum the displacement is equal to amplitude. Then kinetic energy will be

EASY

Science>Physics>Work and Energy>Energy Transformation

Blocks of masses

m, 2 m, 4 m

and

8 m

are arranged in a line of a frictionless floor. Another block of mass

m

, moving with speed

υ

along the same line (see figure) collides with mass

m

in perfectly inelastic manner. All the subsequent collisions are also perfectly inelastic. By the time the last block of mass

8 m

starts moving the total energy loss is

p %

of the original energy. Value of

p

is close to:
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MEDIUM

Science>Physics>Work and Energy>Energy Transformation

An asteroid of mass

m

is approaching earth, initially at a distance

10 R_{e}

with speed

v_{i} .

It hits Earth with a speed

v_{f},

(R_{e}

and

M_{e}

are radius and mass of earth

)

, then

MEDIUM

Science>Physics>Work and Energy>Energy Transformation

A mass of $0.5 kg$ moving with a speed of $1.5 m s^{- 1}$ on a horizontal smooth surface, collides with a nearly weightless spring of force constant $k = 50 N m^{- 1}$ . The maximum compression of the spring would be