NCERT Class-9 Science Solutions: Chapter 11-Work and Energy Part 2 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 8:

Water stored in a dam possesses

  1. No energy
  2. Electrical energy
  3. Kinetic energy
  4. Potential energy

Answer: D

Question 9:

A body is falling from a height . After it has fallen a height , it will possess

  1. Only potential energy
  2. Only kinetic energy
  3. Half potential and half kinetic energy
  4. More kinetic and less potential energy

Answer: C

Image Alf Potential and Half Kinetic Energy

Short Answer Questions

Question 10:

A rocket is moving up with a velocity . If the velocity of this rocket is suddenly tripled, what will be the ratio of two kinetic energies?

Answer:

Initial velocity

Initial kinetic energy

Final kinetic energy (K. E.)

Question 11:

Avinash can run with a speed of against the frictional force of , and Kapil can move with a speed of against the frictional force of . Who is more powerful and why?

Answer:

Given, force applied by Avinash = 10 N

Speed of Avinash = 8 ms-1 ′

Power of Avinash

Now, force applied by Kapil

Speed of Kapil

The power of Kapil

Since, Avinash has more power W than Kapil. Therefore, Avinash is more powerful.

Question 12:

A boy is moving on a straight road against a frictional force of . After travelling a distance of he forgot the correct path at a roundabout (Figure) of radius . However, he moves on the circular path for one and half cycle and then he moves forward up to . calculate the work done by him.

Image the Round About

Answer:

He moves on the circular path for one and half cycle . he forgot the correct path at a round about. He moves on the circular path for one and half cycle so the displacement

So total displacement

We have,

Therefore,