1. What will be the kinetic energy of a body when its mass is made four-time and the
velocity is doubled?
2. Write down the energy transformation taking place
(a) In electric bulb
(b) In torch
(c) In the thermal power station
(d) In solar cell
(e) Electric heater
3. A boy pushes a book by applying a force of 40 N. Find the work done by this force as
the book is displaced through 25 cm along the path.
4. What is work done by a force of gravity in the following cases?
(a) Satellite moving around the Earth In a circular orbit of radius 35000 km.
(b) A stone of mass 250 g is thrown up through a height of 2.5 m
5. A bus of mass 10,000 kg is moving with a velocity 90 km/h. Calculate the work done to stop this bus
6. A girl having a mass of 35 kg sits on a trolley of mass 5 kg. The trolley is given an
initial velocity of 4 m/s by applying a force. The trolley comes to rest after traversing
distance of 16 m.
(a) How much work is done on the trolley?
(b) How much work is done by the girl?
a
7. State the law of conservation of energy. Show that the energy of a freely falling body is
conserved. 8. Avinash can run with a speed of 8 m/s against the frictional force of 10 N, and Kapil
can move with a speed of 3 m/s against the frictional force of 25 N. Who is more powerful
and why?
9. What is power? How do you differentiate kilowatt from kilowatt-hour? The Jog falls in
Karnataka state are nearly 20 m high. 2000 tonnes of water falls from it in a minute.
Calculate the equivalent power if all this energy can be utilized. (g = 10 ms 2 10. What happens to the kinetic energy when:
a. the mass of the body is doubled at constant velocity?
b. the velocity of the body is doubled at constant mass? C. the mass of the body is doubled but velocity is reduced to one fourth
Answers
Answer:
1) 8mv^2
3) 1000 J
Explanation:
1) Kinetic energy is given by = 1/2 mv^2
So when mass becomes four times and velocity becomes double then it's formula will be
K.E = 1/2mv^
= 1/2*(4m) ( 2v)^2
= 1/2 * 4m * 4v^2
= 1/2*16 mv^2
= 8mv^2
2) a) In Electric bulb - Electrical energy is converted into light energy and somewhat heat energy.
b) In torch- Chemical energy is converted into light and heat energy.
c) In the thermal power station- Heat energy is converted into electrical energy or power.
d) In solar cell - Heat or light energy is converted into electrical energy.
e) Electric heater- Electrical energy is converted into heat energy.
3) Force Given = 40 N
Displacement along the path= 25 cm
Applying formula
Work done= Force*displacement*cos theta
As displacement is along the path so theta(angle) is 0°
So work done= Force*displacement
= 40*25
= 1000 J
4) Rest is too easy