Work and Energy Worksheet8

A man X goes to the top of a building by a vertical spiral staircase. Another man Y of the same mass goes to the top of the same building by a slanting ladder. Which of the two does more work against gravity and why ?

When a ball is thrown inside a moving bus, does its kinetic energy depend on the speed of the bus ? Explain.

A bullet of mass 15 g has a speed of 400 m/s. What is its kinetic energy ? If the bullet strikes a thick target and is brought to rest in 2 cm, calculate the average net force acting on the bullet. What happens to the kinetic energy originally in the bullet ?

Name the commercial unit of measurement of energy.

Define kilowatthour.

Name two units of power bigger than watt.

Define the term 'watt'.

How many watts equal one horse power ?

Name the physical quantity whose unit is watt.

What is the power of a body which is doing work at the rate of one joule per second ?

A body does 1200 joules of work in 2 minutes. Calculate its power.

How many joules are there in one kilowatthour ?

What is the common name of '1 kWh' of electrical energy ?

A cell converts one form of energy into another form. Name the two forms.

Name the device which converts electrical energy into mechanical energy.

Name the devices or machines which convert:
1. Mechanical energy into electrical energy.
2. Chemical energy into electrical energy.
3. Electrical energy into heat energy.
4. Light energy into electrical energy.
5. Electrical energy into light energy.
6. Electrical energy into sound energy.
7. Heat energy into kinetic energy (or mechanical energy).
8. Chemical energy into kinetic energy (or mechanical energy).
9. Chemical energy into heat energy.
10. Light energy into heat energy.

A trolley is pushed along a road with a force of 400 N through a distance of 60 m in 1 minute. Calculate the power developed.

What kind of energy transformations take place at a hydroelectric power station ?

What kind of energy transformations take place at a coalbased thermal power station ?

A man weighing 500 N carried a load of 100 N up a flight of stairs 4 m high in 5 seconds. What is the power ?
Answer:

Both the men, X and Y, do equal amount of work against gravity because irrespective of whether they reach the top of building by using a spiral staircase or a slanting ladder, the vertical distance moved by them against gravity is the same

Kinetic energy = (1/2)mv^{2}
Yes, the kinetic energy of a ball thrown inside a moving bus depends on the speed of the bus. Because the speed of bus adds up to the speed with which the ball is thrown inside the moving bus.

1200 J ; 6 × 104 N ; Kinetic energy will be converted mainly into heat energy by friction.

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Kilowatt (kW) and Megawatt (MW)

1 watt is the power of an appliance which consumes energy at the rate of 1 joule per second.
1 watt = (1 joule/1 second) OR 1W = (1J/1S)
So 1 Watt = 1 joule per second

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Power

1 W

10 W

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Unit of electricity

Chemical energy into Electrical energy

Electric motor

1. Electric generator (Alternator or Dynamo)
2. Cell (or Battery)
3. Electric iron
4. Solar cell
5. Electric bulb
6. Speaker (as in radio)
7. Steam engine
8. Car engine
9. Gas stove
10. Solar water heater

400 W

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480 W