Work, Energy and Power 1

Considered Formulas

Example 1

A man moves a stone by a force of 45 N to distance of 4 m long. What is the work done by the man?

Solution

Example 2

Abu Nufayl lifts a sack of rice by a force of 250 N against gravity to 2 m high. Calculate his work done

Solution

Example 3

A car of mass 1000 Kg moves at a velocity of 5 m/s. calculate the kinetic energy possessed by the car.

Solution

Example 4

Find the kinetic energy of the glass marble of mass 24 g travelling at a speed of 40 m/s.

Solution

Example 5

A parcel of mass 36 Kg rests at the top of building 6 m high. Calculate the Potential energy possessed by The parcel. (Use acceleration due to gravity = 10 m/s²)

Solution

Example 6

A mango of mass 50 g falls from tree 4 m high. If it moves at velocity of 80 m/s just before reaching the ground, calculate Potential energy possessed by the mango before falling (Use acceleration due to gravity = 10 m/s²)

Solution

Example 7

A man moves a stone by a force of 45 N to distance of 4 m long in 3 seconds. Calculate power of the man?

Solution

Example 8

How much power is required to accelerate a 1000 kg car from rest to 6 m/s in 8 s?

Solution

EXERCISE

1. A sack of maize which weights 800 N is lifted to height of 2 m. What work done against gravity
2. How much work is done to lift a 70 N weighted object a distance of 5 m and hen hold it at that height for 10 s
3. A force of 80 N pulls a box along a smooth and level ground a distance of 5 m. Calculate the work done by force.
4. An object has a mass of 5 kg. What is its kinetic energy if its speed is
a)      5 m/s
b)      10 m/s
5. What is the kinetic energy of a 12 g bullet travelling at 320 m/s?
6. Sumaytah has a mass of 80 kg. If she runs at a speed of 10 m/s. calculate her kinetic energy 
7. A stone of 2 kg falls from a height of 25 m above the ground.  Calculate potential possessed by the stone before falling (Use acceleration due to gravity = 10 m/s²)
8. A form two student lift a 400 g box to a top of window 1.5 m high for 2 seconds. Calculate potential possessed by the student (Use acceleration due to gravity = 10 m/s²)
9. A 2 kg object is at rest on a table 1.2 m above the floor. The ceiling in the room is 2.8 m above the floor



What is the potential energy possessed by the object on the top of the table?
10. A pump raises 100 kg of water through a height of 30 m in 10 s. What is the power developed by the pump? (Use acceleration due to gravity = 10 m/s²)
11. A 50 kg girl runs up a staircase of 75 cm high in 5 seconds. Find 
a)      Work done against gravity by the girl
b)      Power she uses to run
(Use acceleration due to gravity = 10 m/s²)


12. What is the power required to move a 100 g stone travelling at 20 m/s in 4 seconds?