WORK, ENERGY AND POWER
1.
A car has a kinetic energy
store of 64800 J. It is travelling at a speed of 12 m/s. Calculate the mass of
the car.
2.
A ball of mass 100 g is
thrown vertically upwards with a speed of 15 m/s. What is the maximum height the
ball reaches?
3.
Two students have an
argument about who is more powerful. Peter says he is more powerful because he
is bigger. Hannah says she is powerful because she is quicker.
To settle the argument, they run
up stairs of height 4.5 m. use the information about their weights and times to
settle the argument.
|
|
Weight in N
|
Fastest time in s
|
|
Peter
|
760
|
3.80
|
|
Hannah
|
608
|
3.04
|
4.
A boy with a weight of 600
N climbs up the Eiffel Tower. The Eiffel Tower has a height of 300 m. calculate
the work the boy does against gravity.
5.
a) An electric motor is
used to raise a 0.1 Kg mass vertically upwards. If the mass gains 2 J of
gravitational potential energy, calculate the height it is raised through.
b) If the electric motor has a
power of 1.5 W. Calculate the time taken to raise the load
6. At its highest point A 1.2m a pendulum of mass 0.8kg is reached, what;
a)
Velocity swings at lowest point
b)
Velocity at 0.9m
c)
Height at 2m/s
7.
A 50kg girl runs up a
staircase of 50 steps each step is 15cm in height in 5s. Find
i.
Work done against
gravity by the girl
ii.
Power she uses to run
8.
A mango of mass 80 grams is
dropped from a height of 6 m. Calculate the
a) Total energy of the system
b) Kinetic energy when it is half way
c) Velocity of the mango at the half way
d) Height of the mango at which travels 6 m/s
e) Potential energy possessed by the mango at which travels 6 m/s
9.
A hoist operated by an
electric motor has a mass of 500 kg. It raises a load of 300 kg vertically at a
steady speed of 0.2 m/s. Frictional resistance can be taken to be constant at
1200N. What is the power required?
10.
A body released from rest
at a certain height above the ground. If the body strikes the ground with a
velocity of 60 m/s, calculate
i)
The height from which the
body was released
ii) The time taken by the body to strike the ground.
11.
A man whose mass is 75Kg walks up a
flight of 12 steps each 20 cm high in 5 seconds. Find the power he develops in
watt.
12.
A body of mass 50Kg is
raised to a height of 2m above the ground.
a) What is its potential energy?
b) If the body is allowed to fall, find the kinetic energy;
i)
When half-way down;
ii) Just before impact with the ground.
13.
A ball of mass of 1Kg is
dropped from a height of 7m and rebound to a height of 4.5m. Calculate;
i)
Its kinetic energy just
before impact
ii) Its initial rebound velocity and kinetic energy
iii) Account for the loss of kinetic energy on impact.
14. A car of mass 1000Kg is travelling along a straight
road at a constant velocity of 15 metres per second. The engine then develops
3.0 Kilowatts. Calculate;
iv) The force resisting the motion
v) If the engine is switched off, how much energy will the car lose
in coming to rest?
vi) Describe the energy changes in this process
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