Heena Sharma, Shubhankat Vats and, Rashmi Gupta Solutions for Chapter: Work and Energy, Exercise 6: Challengers*

The energy absorbed by a solar panel is used to charge a battery. During the day, the battery stores$1.6 \mathrm{J}$of energy each second. At night the battery is used to light a$1.2 \mathrm{W}$ lamp for $1800 \mathrm{s}.$ What is the minimum time for which the battery must be charged within the day?

A force of $5 \mathrm{N}$acts on a $1.5 \mathrm{kg}$ body initially at rest. The work done by the force during the first second of motion of the body is

A force is applied by an engine of a train of mass $205\times {10}^6 \mathrm{kg}$ changes its velocity from$5 \mathrm{m}/\mathrm{s} \mathrm{to} 25 \mathrm{m}/\mathrm{s}$.  Power of engine is

Natural length of a spring is$60 \mathrm{cm}$ and its spring constant is$4000 \mathrm{N}/\mathrm{M}.$ A mass of $20 \mathrm{kg}$is hung from it. The extension produced in the spring is, (take,$\mathrm{g}=9.8\mathrm{m}/{\mathrm{s}}^2$)

A lorry and a car moving with the same K E are brought to rest by applying the same retarding force, then;

The figure shows the variation of force and displacement. Find the value of work done at the end of the displacement $30 \mathrm{m}$is 

Water falls from a height of $60 \mathrm{m}$ at the rate of $15 \mathrm{kg}$ to operate a turbine. The losses due to frictional forces are $10 \%$ of energy. How much power is generated by the turbine? (take,$\mathrm{g}=10\mathrm{m}/{\mathrm{s}}^2$)

A block mass of $10 \mathrm{kg}$ is dropped from a height of $10 \mathrm{m}$ from the earth's surface and it falls onto a vertical helical spring of stiffness $5000 \mathrm{N}/\mathrm{M}$ and length $50 \mathrm{cm}$. The compression of the spring is (Take $\mathrm{g}=10 \mathrm{m}/{\mathrm{s}}^2$)