NCERT Class9 Science Solutions: Chapter 11Work and Energy Part 2
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Question 8:
Water stored in a dam possesses

No energy

Electrical energy

Kinetic energy

Potential energy
Answer: D
Question 9:
A body is falling from a height. After it has fallen a height, it will possess

Only potential energy

Only kinetic energy

Half potential and half kinetic energy

More kinetic and less potential energy
Answer: C
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 ms1 ‘
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.
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,