Physics>Change>Energy>Forms of Energy

EASY

Earn 100

Which of the following energy travels in the form of an electromagnetic wave?

50% studentsanswered this correctly

Important Questions on Energy

MEDIUM

Physics>Change>Energy>Forms of Energy

Two equal masses are attached to the two ends of a spring of spring constant

k

. The masses are pulled out symmetrically to stretch the spring by a length

x

over its natural length. The work done by the spring on each mass is

HARD

Physics>Change>Energy>Forms of Energy

The gravitational field due to a mass distribution is

E = \frac{K}{x^{2}}

in the

x -

direction. (

K

is a constant). Taking the gravitational potential to be zero at infinity, its value at a distance

x

is

MEDIUM

Physics>Change>Energy>Forms of Energy

An electron and a proton are detected in a cosmic ray experiment, the first with kinetic energy

10 keV

, and the second with

100 keV

. Which is faster, the electron or the proton? Obtain the ratio of their speeds. (electron mass

= 9.11 \times 10^{- 31} kg

, proton mass

= 1.67 \times 10^{- 27} kg

,

1 eV = 1.60 \times 10^{- 19} J

)

HARD

Physics>Change>Energy>Forms of Energy

Three identical stars, each of mass

M,

form an equilateral triangle (stars are positioned at the corners) that rotates around the centre of the triangle. The system is isolated and the edge length of the triangle is

L .

The amount of work done, that is required to dismantle the system is

EASY

Physics>Change>Energy>Forms of Energy

A body of mass

m kg

starts falling from a point

2 R

above the Earth's surface. Its kinetic energy when it has fallen to a point

R

above the Earth's surface is [

R -

Radius of Earth,

M —

Mass of Earth,

G —

Gravitational Constant]

MEDIUM

Physics>Change>Energy>Forms of Energy

Two springs have their force constant

k_{1}

and

k_{2} (k_{1} > k_{2})

. When they are stretched with the same force,

EASY

Physics>Change>Energy>Forms of Energy

Two springs

A

and

B

(k_{A} = 2 k_{B})

are stretched by applying forces of equal magnitudes at the four ends. If the energy stored in

A

is

E

, then that in

B

is

MEDIUM

Physics>Change>Energy>Forms of Energy

A book is lifted from the floor and is kept in an almirah. One person says that the potential energy of the book is increased by

20 J

and the other says it is increased by

30 J

. Is one of them necessarily wrong?

EASY

Physics>Change>Energy>Forms of Energy

The gravitational potential energy of a body of mass

m

at the Earth's surface is,

- m g R_{e}

. Its gravitational potential energy at a height

R_{e}

from the Earth's surface will be (Here

R_{e}

is the radius of the earth)

EASY

Physics>Change>Energy>Forms of Energy

Which type of energy is produced by the movement of electric charges?

HARD

Physics>Change>Energy>Forms of Energy

An object of mass

m

is raised from the surface of the earth to a height equal to the radius of the earth, that is, taken from a distance

R

to

2 R

from the centre of the earth. What is the gain in its potential energy?

HARD

Physics>Change>Energy>Forms of Energy

Four particles each of mass $M$ are located at the vertices of a square with side length $L$ . The gravitational potential due to this at the centre of the square is

EASY

Physics>Change>Energy>Forms of Energy

When a long spring is stretched by

2 cm

, its potential energy is

U

. If the spring is stretched by

10 cm

, the potential energy stored in it will be

HARD

Physics>Change>Energy>Forms of Energy

The radius and mass of earth are increased by

0.5 % .

Which of the following statements are true at the surface of the earth?

HARD

Physics>Change>Energy>Forms of Energy

A

1 kg

block situated on a rough incline is connected to a spring of spring constant

100 N m^{- 1}

as shown in Fig. The block is released from rest with the spring in the unstretched position. The block moves

10 cm

down the incline before coming to rest. Find the coefficient of friction between the block and the incline. Assume that the spring has a negligible mass and the pulley is frictionless.
Question Image

Question Image

MEDIUM

Physics>Change>Energy>Forms of Energy

If the mass of the earth is

M

, radius is

R

and gravitational constant is

G

, then work done to take

1 kg

mass from the earth's surface to infinity will be

MEDIUM

Physics>Change>Energy>Forms of Energy

One person says that the potential energy of a particular book kept in an almirah is

20 J

and the other says it is

30 J

. Is one of them necessarily wrong?

MEDIUM

Physics>Change>Energy>Forms of Energy

The gravitational potential energy of a two-particle system is derived in this chapter as $U = - G \frac{m_{1} m_{2}}{r}$ .

Does it follow from this equation that the potential energy for $r = \infty$ must be zero?

Can we choose the potential energy for $r = \infty$ to be $20 J$ and still use this formula? If no, what formula should be used to calculate the gravitational potential energy at separation $r$ ?

EASY

Physics>Change>Energy>Forms of Energy

What is meant by thermal energy?

HARD

Physics>Change>Energy>Forms of Energy

A body of mass

m

rises to height

h = \frac{R}{5}

from the earth's surface, where

R

is earth's radius. If

g

is acceleration due to gravity at earth's surface, the increase in potential energy is