# NCERT Class-9 Science Solutions: Chapter 11-Work And Energy Part 6

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**Question 27:**

Define watt. Express kilowatt in terms of joule per second. A car engine develops for each kg. What force does it exert in moving the car at a speed of ?

**Answer:**

One watt is the power of an agent which does work at the rate of

**Question 28:**

Compare the power at which each of the following is moving upwards against the force of gravity?

A butterfly of mass that flies upward at a rate of .

A squirrel climbing up on a tree at a rate of .

**Answer:**

Hence, the power with which the squirrel is climbing is much higher than that of a butterfly flying.