A particle with total mechanical energy which is small and negative is under the influence of a one dimensional potential U x = x 4 4 - x 2 2 J , where x is in meters. At time t = 0 s , it is at x = - 0 . 5 m . Then at a later time it can be found,

between x = - 1 . 0 m to x = 0 . 0 m

between x = - 1 . 0 m to x = 1 . 0 m

between x = 0 . 0 m to x = 1 . 0 m

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A ball of mass $m$ is dropped from a cliff of height $H$ . The ratio of its kinetic energy to the potential energy when it has fallen through a height $\frac{3}{4} H$ is

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Important Questions on Work, Energy and Power

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General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

A body is moving unidirectionally under the influence of a source of constant power. The square of its displacement in time

t

is proportional to

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General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

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:

MEDIUM

General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

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

EASY

General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

If a spring of spring constant

200 N m^{- 1}

is compressed by

5 cm

, then the energy stored in the spring is

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General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

A particle with total mechanical energy which is small and negative is under the influence of a one dimensional potential

U (x) = \frac{x^{4}}{4} - \frac{x^{2}}{2} J

, where

x

is in meters. At time

t = 0 s

, it is at

x = - 0.5 m

. Then at a later time it can be found,

EASY

General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

A block of mass

100 g

moving at a speed of

2 m s^{- 1}

compresses a spring through a distance

2 cm

before its speed is halved. Find the spring constant of the spring

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General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

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

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General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

A particle is released from a height

H

. At a certain height its kinetic energy is half of its potential energy with reference to the surface of the earth. Height and speed of the particle at that instant are respectively

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General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

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}

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General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

A particle

(m = 1 k g)

slides down a frictionless track

(A O C)

starting from rest at a point

A

(height

2 m

). After reaching

C,

the particle continues to move freely in air as a projectile. When it reaches its highest point

P

(height

1 m

), the kinetic energy of the particle (in

J

) is: (Figure drawn is schematic and not to scale; take

g = 10 m s^{- 2}

) ______________.
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General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

The potential energy function for a two dimensional force is given by

U = 3 x^{3} y - 7 x

. The force that acts at the point

(x, y)

is (Take

\hat{i}

and

\hat{j}

as unit vectors along

X

- and

Y

- axes)

HARD

General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

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

HARD

General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

A mass of

2 kg

, initially at a height of

1.2 m

above an uncompressed spring with spring constant

2 \times 10^{4} N m^{- 1},

is released from rest to fall on the spring. Taking the acceleration due to gravity as

10 m s^{- 2}

and neglecting the air resistance, the compression of the spring in

mm

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General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

A uniform chain of mass

M

and length

L

is lying on a smooth horizontal table, with half of its length hanging down. The work done in pulling the entire chain up the table is

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General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

A body is released from a height of

30 m

vertically downwards. The speed of the body at which potential energy is twice that of kinetic energy is (Acceleration due to gravity

= 10 m s^{- 2}

)

HARD

General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

The potential energy

(U)

of a diatomic molecule is a function dependent on

r

(interatomic distance) as

U = \frac{α}{r^{10}} - \frac{β}{r^{5}} - 3

where,

α

and

β

are positive constants. The equilibrium distance between two atoms will be

{(\frac{2 α}{β})}^{\frac{1}{a}},

where

a =

______ .

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General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

The graphs below show the magnitude of the force on a particle as it moves along the positive $X$ -axis from the origin to $X = X_{1}$ . The force is parallel to the $X$ -axis and conservative. The maximum magnitude $F_{1}$ has the same value for all graphs. Rank the situations according to the change in the potential energy associated with the force, least (or most negative) to greatest (or most positive).

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General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

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:

HARD

General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

Consider two masses with

m_{1} > m_{2}

connected by a light inextensible string that passes over a pulley of radius

R

and moment of inertia

I

about its axis of rotation. The string does not slip on the pulley and the pulley turns without friction. The two masses are released from rest separated by a vertical distance

2 h .

When the two masses pass each other, the speed of the masses is proportional to

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General Science>Physics>Work, Energy and Power>Various Forms of Energy and Law of Conservation of Energy

The potential energy of a system increases if work is done

A ball of mass m is dropped from a cliff of height H. The ratio of its kinetic energy to the potential energy when it has fallen through a height 34H is

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A ball of mass $m$ is dropped from a cliff of height $H$ . The ratio of its kinetic energy to the potential energy when it has fallen through a height $\frac{3}{4} H$ is