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Subject: Science, asked on on 11/2/14

I have some doubts in the following questions:

Chapter : WORK , ENERGY AND POWER

1. A body of mass 2 kg is dropped from the top of a tower of height 100 m. If

the acceleration due to gravity is 10 m/s2

calculate the K.E at the end of 5

seconds.

2. A body of mass 2 kg is thrown vertically upwards with an initial velocity of

20 m/s2

. What will be its P.E at the end of 2 s . ( Take g as 10 m/s2

)

3. A body is thrown vertically upwards .its velocity keeps decreasing. What

happens to its K.E as velocity becomes zero. Find the energy present in an

object of mass 10 kg when it is at a height of 6m above the ground. Given

g= 9.8 m/s2

.

4. A porter lifts a luggage of 15 kg from the ground and puts it on her head 2m

above the ground. Calculate the work done by her on the luggage. (Take g=

10 m/s2

).

5. A rocket of mass 3x 10 6

kg mass takes off from a launching pad and attains

a velocity of 1 km/h at an attitude of 25 km. Calculate the P.E and K.E .

(Take g=10m/s2

)

6. An object of mass 40 kg is raised to a height of 5m above the ground. What

is the P.E. if the object is allowed to fall, find the K.E when it is half way

down. Take g as 10 m/s2

.

7. A boy of mass 40 kg runs up a flight of 15 steps, each 15 cm high in 10 s.

Find the work done and the power developed by him. (Take g=10m/s2

)

8. Two bodies of equal masses move with uniform velocities of v and 3v

respectively. Find the ratio of their kinetic energies.

9. What is the work done to increase the velocity of a car from 30 km/h to

60 km/h. Let the mass of the car be 1500 kg.

10. On a level road, a scooterist applies brakes to slow down from a speed of

36 km/h to 18 km/h. Find the work done by the brakes, assuming the mass

of the empty scooter to be 86 kg and that of the person and petrol equal to

64 kg.

11. How much time will a pump of 1 kW power take to lift 500kg of water to

height of 40 m ? (Take g=10m/s2

)

12. A horse exerts a pull on the cart of 300 N so that the horse-cart system

moves with a uniform speed of 18 km/h on a level ground. Calculate the

power developed by the horse in watt and also find its equivalent in

horsepower.

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