Dhiren M Doshi Solutions for Chapter: Work and Energy, Exercise 8: Exercises

A boy of mass $45 \mathrm{kg}$ climbs up $20$ steps in $20$ seconds. If each step is $25 \mathrm{cm}$ high, calculate the power used in climbing. (take $\mathrm{g} = 10 \raisebox{1ex}{$\mathrm{m}$}\!\left/ \!\raisebox{-1ex}{${\mathrm{s}}^2$}\right.$)

A stone of mass $3 \mathrm{kg}$ is lying on the edge of a cliff of $100 \mathrm{m}$ height from the ground level. If the stone is dropped, calculate the maximum energy released by the stone. (take $\mathrm{g}=9.8 \raisebox{1ex}{$\mathrm{m}$}\!\left/ \!\raisebox{-1ex}{${\mathrm{s}}^2$}\right.$)

A body is raised to a height of $10 \mathrm{m}$ when the energy spent is $1000 \mathrm{J}$. Calculate the mass of the body. (take $\mathrm{g}=10 \raisebox{1ex}{$\mathrm{m}$}\!\left/ \!\raisebox{-1ex}{${\mathrm{s}}^2$}\right.$)

What is the work done to increase the velocity of a car from $36 \raisebox{1ex}{$\mathrm{km}$}\!\left/ \!\raisebox{-1ex}{$\mathrm{h}$}\right.$ to $72 \raisebox{1ex}{$\mathrm{km}$}\!\left/ \!\raisebox{-1ex}{$\mathrm{h}$}\right.$, if the mass of the car is $1500 \mathrm{kg}$?

Manisha was discussing question paper with her friend Simran. She felt exhausted after some time.

a. In terms of physics, Manisha has done no work. Give reasons.

b. What values we learn from Manisha?

In a tug of war, Amina's team is slowly giving way to Ruby's team.

a. What work is being done, and by whom?

b. What values are learnt from the tug-of-war game? 

Arun wanted to make a science model. Karan helped him to make a windmill model.

a. How can moving air run a windmill?

b. What values do we learn from Karan?

Faizan asked his teacher why the sun is the ultimate source of energy?

a. Name any two sources of energy derived from the sun's energy.

b. What values do we learn from Faizan?