Work

Johnny and his sister Jane race up a hill. Johnny weighs twice as much as Jane and takes twice the time as long as Jane to reach the top. Compared to Jane:

A block of mass $50 \mathrm{kg}$ just slides over a distance of $1 \mathrm{m}$. If the coefficient of friction between their surfaces is $0.2$, the work done against friction is

A cubical vessel of height $1 \mathrm{m}$ is full of water. What is the amount of work done in pumping water out of the vessel?

[Take $g=10 {\mathrm{ms}}^{-2}$]

When a force is applied on a moving body, its motion is retarded. Then the work done is

Deduce work energy theorem for constant force.

Explain work.

A force of $\overrightarrow{F}=(2\hat{i}+3\hat{j}+4\hat{k}) N$ is applied on a particle displacing it by a distance $\overrightarrow{\mathrm{d}}=(3\hat{\mathrm{i}}-2\hat{\mathrm{j}}+\hat{\mathrm{k}})\mathrm{m}$. Calculate the work done by the force.

The amount of work done by the centripetal force when the earth revolves around the sun is _____.

(Choose from zero/non-zero)

Force of $4 \mathrm{N}$ is applied on a body of mass $20 \mathrm{kg}$. Find the work done in Joules in $3$rd second.

A man spends $6.4 \mathrm{k} \mathrm{J}$ energy in displacing a body by$64 \mathrm{m}$ in the direction in which he applies force, in $2.5 \mathrm{s}$. The force applied and the power spent (in hp) by the man respectively are:

An electric motor of power $100 \mathrm{W}$ is used to drive the stirrer in a water bath. If $50\%$ of the energy supplied to the motor is spent in stirring the water, calculate the work done (in joules) on water in one minute.

Whenever a force is applied, work is done.

Force acting opposite to the direction of motion of a body does negative work on it.

The power of heart which beats $72$ times in a minute is $1.2 \mathrm{kW}$. Calculate the work done (in joules) by the heart for each heartbeat.

Force and displacement are inclined to each other at an angle of $120°$. Will the work done be positive or negative?

A man pulls a bucket out of a well by means of a rope. The work done by the man is

The work done by a force is _____ (positive/ negative/ zero) if the displacement in the direction of the force increases.

Describe the properties of work done.