Worksheet solutions for chapter: Work and Energy for class 9 are provided.
(2) Define energy?
Ans- The capacity of an object to do work is known as energy.
The unit of energy is same as work because it measures in work. Therefore the SI unit of the energy is joule.
1 j is the energy required to do 1 j of work. Sometime energy can be measured in kilo joule (kj).
1 kj = 1000 j
(3) What does a “unit” means?
Ans- The electricity energy used in household, industries and commercial establishments are expressed in kw h.
Our electricity energy bill shows consumption in “units”.
Here, 1 unit of electricity consumption = 1 kilowatt hour
(6) In which fig given below work done will be greater?
Ans- In both figure work done will be equal to the potential energy. The work done by the gravity depends on the difference in vertical heights of the initial and final positions of the object and not on the path along which the object is moved.
In fig (i) ,
Potential energy = mgh
In fig (ii)
Potential energy = mgh
Hence, work done in both conditions will be same.
(7) What is the energy transformation in stretched bow and arrow?
Ans- When a bow is stretched, potential energy stored in it. That potential energy transform in kinetic energy when we throw off the arrow.
(8) There are two children A and B. Both weigh same. They climb a rope of 8 m. Child A completes climbing in 10 second while child B completes climbing in 5 second.
(i) Who has done more work?
(ii) Who has done more work in 1 second?
Ans– (i)Both children have same weight, ie, they have same mass. Therefore, same gravitational force is applied on both children.
They climbed same distance, ie, their displacement is equal.
Therefore, they have done same work. Time taken in completing work is not count in calculating work done.
(ii) Child A has done more work in 1 second because he has completed his task in less time than child B.
(10) A porter carry 10 kg load on its head and stand at a place for half an hour and waiting for the train. Another porter also carry 10 kg load and walk 100 m distance. Which porter has done work and why?
Ans- First porter is not doing any work because he is standing at one place and not displacing. Therefore work done by him is zero.
But second porter is doing work because he is displacing.