Q 1.When do we say that work is done?
Q 2. When displacement is in a direction opposite to the direction of force applied, what is the type of work done?
Q 3. Archana tried to push a heavy rock of 200 kg for 80 seconds but could not move it. Find the work done by Archana after 80 seconds.
Q 4. Write the expression for the kinetic energy of an object.
Q 5. State the energy possessed by a raised hammer before it hits an iron nail.
Q 6. An object of mass 2 kg is raised to a height of 1.5 m above the earth by Amit and Rakesh as shown in the diagram. (given g = 9.8m/s2)
(i) Who does more work? Justify your answer.
(ii) Calculate the work done in both the situations.
Amit
Rakesh
Q 7. What will happen to the kinetic energy of the body if mass remains the same, and
(i) velocity of the body is doubled?
(ii) velocity of the body is halved?
Q 8. A bullet of mass 15 g has a speed of 400 m/s. What is its kinetic energy?
Q 9. Define one joule of work.
Q 10.58800J energy is utilized in lifting a mass of 50 kg. Find out the height to which the mass was lifted. (Given, g = 9.8m/s2)
Q 11.What is the work to be done to increase the velocity of the car from 10 m/s to 20 m/s if the mass of the car is 1000 kg?
Q 12.State the law of conservation of the energy?
Q 13.Rachna states that law of conservation of energy does not remain true all the time and has certain exceptions. For example, when an object falls down from a certain height, its potential energy does not remain same, but decreases progressively. Is Rachna correct? Justify your answer.
Q 14.Name the device which converts:
a.Chemical energy into electrical energy
b.Light energy into electrical energy
c.Electrical energy into heat energy
Q 15.What is average power? Show it symbolically.
Q 16.Differentiate between kilowatt and kilowatt hour.
Q 17.An electric heater is rated 2000 W. Calculate electrical energy consumed by it in
10 hours.
Q 18.A family uses 250 units (kWh) of electrical energy during a month. Calculate the electrical energy in joules.
Q 19 A machine does 1920 joule of work in 240 seconds. What is the power of the machine?
Q 20 Two friends, Sam and John, each having weight of 40 kg, go for rock climbing. Sam climbs to a height of 3 m in 10 s and John covers the same height in 12s.
a.Is the work done by Sam and John equal? Why?
b.Who has more power? Why?
c.Calculate the power of Sam and John.
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