English Medium Class 9 - CBSE Question Bank Solutions

What is power?

Define 1 watt of power.

A lamp consumes 1000 J of electrical energy in 10 s. What is its power?

Define average power.

A battery lights a bulb. Describe the energy changes involved in the process.

What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.

A person holds a bundle of hay over his head for 30 minutes and gets tired. Has he done some work or not? Justify your answer.

An electric heater is rated 1500 W. How much energy does it use in 10 hours?

Find the energy in joules consumed in 10 hours by four devices of power 500 W each.

Is the following statement true or false :
A rocket can propel itself in a vacuum.

What is the force which produces an acceleration of 1 m /s²  in a body of mass 1 kg ?

A girl weighing 25 kg stands on the tloor. She exerts a downward force of 250 N on the floor. What force does the floor exert on her ?

Fill in the following blanks with suitable words :

Forces in a Newton’s third law pair have equal _____________ but act in opposite _____________.

Why does a gunman get a jerk on firing a bullet ?

If action is always equal to reaction, explain why a cart pulled by a horse can be moved.

Explain how a rocket works.

Do action and reaction act on the same body or different bodies ? How are they related in magnitude and direction ? Are they simultaneous or not ?

If a man jumps out from a boat, the boat moves backwards. Why ?

Why is it difficult to walk on a slippery road ?

Explain why, a runner presses the ground with his feet before he starts his run.