**TEST**

**CLASS XI**

**WORK, ENERGY & POWER**

**Very Short Answer Type Questions:Â [Â ****1 Marks Questions ]**

Q1. What is the work done when a body is moved horizontally along a frictionless surface?

Q2. What is the work done on a body moving in a circular path?

Q3. Define 1 watt.

Q4. What is kinetic energy?

Q5. What will happen to the Kinetic Energy of a body if its velocity is doubled?

**Short Answer Type Questions: [ 2 Marks Questions ]**

Q6. A person holds a body of mass 20 kg over his head for 10 sec. Has he done any work? Justify your answer.

Q7. A free falling body stops on reaching the ground. What happens to its kinetic energy?

Q8. How are K.E. and momentum related?

Q9. Is it possible that a body be in accelerated motion under a force and no work is being done by the force?

Q10. When an arrow is shot from its bow, it has K.E. From where does it get the K.E.?

**NumericalÂ [ 3 Mark Questions ]**

Q11. A force acting on a 20 kg mass changes its velocity from 5 m/s to 2 m/s. Calculate the work done.

Q12. The K.E. of an object of mass m moving with a velocity of 5 m/s is 25 J. What will be its K.E. when its velocity is doubled? What will be its K.E when its velocity is increased 3 times?

Q13. An object of mass 12 Kg is at a certain height above the ground. If the gravitational P.E. is 480 J, find the height at which the object is w.r.t the ground (g = 10 m/s^{2})

Q14. An object of mass 40 kg is raised to a height 5 m above the ground. What is its P.E.? If object is allowed to fall, find its K.E. just before touching the ground and also its K.E. when it is half way down.

Q15. What is the work done to increase the velocity of car from 36 km/h to 72 km/h, if the mass = 1500 Kg.

Q16. A man whose mass is 50 kg climbs up 30 steps of a stair in 30 s. If each step is 20 cm high, calculate the power used in climbing stairs.

**Â ****5 Marks Questions**

Q17. Deduce a formula for K.E of a body.

Q18. State the law of conservations of energy. Show that when a body falls from a height the total mechanical energy remains same.

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