Energy

An object of mass, $m$ is moving with a constant velocity, $v$. How much work should be done on the object in order to bring the object to rest?  

If a bullet of mass $80 \mathrm{g}$ moves with a velocity of $700 \mathrm{m} {\mathrm{s}}^{-1}$. It penetrates $25 \mathrm{cm}$ into a target which is not moving and then comes to rest. Find the kinetic energy possessed by the bullet and also the average retarding force offered by the target. 

What is gravitational potential energy? Derive its equation.

An electric motor has a power of $2 \mathrm{hp}$ and is used to run water pump. The water pump takes $15 \mathrm{minutes}$ to fill an overhead tank. The capacity of the tank is $1000 \mathrm{l}$ and height is $20 \mathrm{m}$. Find the actual work done by the electric motor to fill the tank. Also find the efficiency of the system. (Density of water = $1000 \mathrm{kg} {\mathrm{m}}^{-3}$ )  (Mass of $1 \mathrm{l}$ of water is $1 \mathrm{kg}$)

Assertion: If velocity of a moving body is increased to double, then its kinetic energy increases four times.

Reason: Kinetic energy is directly proportional to the square of velocity.

The explosion at Krakatoa is estimated to have released the energy equivalent to $200 \mathrm{million} \mathrm{tonnes}$ of TNT. The first nuclear detonation-the Trinity test -yielded an equivalent of $22 \mathrm{thousand} \mathrm{tonnes}$ of TNT. How many times more powerful was the explosion at Krakatoa?

A car travels along a flat road. It has $50 \mathrm{billion} \mathrm{J}$ of kinetic energy. Every second, air resistance and other frictional forces cause it to lose$1 \mathrm{billion} \mathrm{J}$  of energy. If the car is to travel at a constant speed, how much energy will the engine have to convert to kinetic energy every second?

A toy car has a kinetic energy of $10 \mathrm{J}$. It rolls up a slope and at the top it has $3 \mathrm{J}$ of gravitational potential energy and $5 \mathrm{J}$ of kinetic energy. How much energy has the car lost through friction?

Name the kind of energy used in the following.

Name the kind of energy used in the following.

When a driver wants to stop a car, he presses the brake pedal. The brakes applied, which use friction to slow the car to a stop. Which of the following energy transformations occurs as a car brakes?

A driver parks his car on a hill but forgets to put brakes on. The car starts to roll down the hill. Which of the following energy transformation occurs as the car rolls down the hill?

A body of $12 \mathrm{kg}$ mass is placed at a certain height from the surface of earth. If its potential energy is $480 \mathrm{J}$, then what will be its height with respect to earth's surface? $(g=10 {\mathrm{ms}}^{-2})$

Loudspeaker converts electrical energy to _____ (sound/heat) energy.

There is a slight temperature difference between the waterfall at the top and at the bottom because

A stone of mass $500 \mathrm{g}$is thrown vertically upwards with a velocity of $15 \mathrm{m}/\mathrm{s}$. Calculate the potential energy (in joules) at the greatest height.

A body of mass $60 \mathrm{kg}$ has the momentum $3000 \mathrm{kg} {\mathrm{ms}}^{-1}.$ Calculate the kinetic energy and speed of the body.

A ball of mass $0.5 \mathrm{kg}$ slows down from a speed of $5 {\mathrm{ms}}^{-1}$ to that of $2 {\mathrm{ms}}^{-1}$. Calculate the change in kinetic energy of the ball. 

Calculate the kinetic energy of a body of mass $0.1 \mathrm{kg}$and momentum $20 {\mathrm{kgms}}^{-1}.$ (in joules)

A bullet of mass $5 \mathrm{g}$ travels with a speed of $500 {\mathrm{ms}}^{-1}$. If it penetrates a fixed target which offers a constant resistive force of $1000 \mathrm{N}$ to the motion of the bullet, find the initial kinetic energy (in joules) of the bullet.