Problem 1
A body moves through a displacement of 4 m while a force F of 12 Newton acts on it. What is the work done by the force on the body?
A body moves through a displacement of 4 m while a force F of 12 Newton acts on it. What is the work done by the force on the body?
Answer
Work =
force x displacement
W = F x S
W = 12 x 4
W = 48 joule
Problem 2
A block is pulled by a constant force of 40 Newton. If the work done by the force on the block is 680 joule what is the displacement of the block?
Answer
The displacement of the block
W = F x S
680 = 40 x S
S = 680 / 40
S = 17 meter
Problem 3 A force acts on a box and displaces it through 13m in a horizontal surface. The work done by the force on the block is 15.6 joule. Find the magnitude of the force.
Answer
Work = force x displacement
W = F x S
15.6 = F x 13
F = 15,6 / 13
F = 1.2 Newton
Problem 4
Two forces that are F1 = 10 N and F2 = 5 N act on a body in a frictionless floor. The displacement of the body is 5 m, what is the work done by the forces on the body? Answer
W = (F1 + F2) x S
W = (10 + 5) x 5
W = 15 x 5
W = 75 joule
Problem 5
A boy lifts up a book from the floor to the table. The mass of the book is 300 gram and the height of the table is 80 cm.
Find the work done by the boy when the acceleration due to gravity is 10 m/s2
Answer
Finding the work done by calculating the difference of gravitational potential energy of the book, where the gravitational potential energy is Ep = m x g x h
W = Δ Ep
W = m x g x h
W = 0,300 x 10 x 0,80
W = 2,4 joule
Problem 6
A boy of 450 N of weight climbs a wood steps with a length of 3 m. The boy takes 6 seconds to get the end of the steps. What is the power done by the boy on this activity.
Answer
The power (P), the work (W) and the time (t) relationship:
P = W/t
where W = (weight of the boy) x (the boy displacement) = 450 x 3 = 1350 joule
So then :
P = W/t
P = 1350 / 6
P = 225 watt
Problem 7
In two minutes the energy dissipated by a lamp is 3000 joule. Find the power of the lamp.
Answer
The data, 2 minutes = 120 sec
P = W/t
P = 3000 / 120
P = 25 watt
Problem 8
A box of 50 Newton of weight is brought by a boy from A to B and then brought back to A.
What is the work done by this boy?
Answer
W = 0 joule
(There is no displacement of the box)
W = F x S
W = 12 x 4
W = 48 joule
Problem 2
A block is pulled by a constant force of 40 Newton. If the work done by the force on the block is 680 joule what is the displacement of the block?
Answer
The displacement of the block
W = F x S
680 = 40 x S
S = 680 / 40
S = 17 meter
Problem 3 A force acts on a box and displaces it through 13m in a horizontal surface. The work done by the force on the block is 15.6 joule. Find the magnitude of the force.
Answer
Work = force x displacement
W = F x S
15.6 = F x 13
F = 15,6 / 13
F = 1.2 Newton
Problem 4
Two forces that are F1 = 10 N and F2 = 5 N act on a body in a frictionless floor. The displacement of the body is 5 m, what is the work done by the forces on the body? Answer
W = (F1 + F2) x S
W = (10 + 5) x 5
W = 15 x 5
W = 75 joule
Problem 5
A boy lifts up a book from the floor to the table. The mass of the book is 300 gram and the height of the table is 80 cm.
Find the work done by the boy when the acceleration due to gravity is 10 m/s2
Answer
Finding the work done by calculating the difference of gravitational potential energy of the book, where the gravitational potential energy is Ep = m x g x h
W = Δ Ep
W = m x g x h
W = 0,300 x 10 x 0,80
W = 2,4 joule
Problem 6
A boy of 450 N of weight climbs a wood steps with a length of 3 m. The boy takes 6 seconds to get the end of the steps. What is the power done by the boy on this activity.
Answer
The power (P), the work (W) and the time (t) relationship:
P = W/t
where W = (weight of the boy) x (the boy displacement) = 450 x 3 = 1350 joule
So then :
P = W/t
P = 1350 / 6
P = 225 watt
Problem 7
In two minutes the energy dissipated by a lamp is 3000 joule. Find the power of the lamp.
Answer
The data, 2 minutes = 120 sec
P = W/t
P = 3000 / 120
P = 25 watt
Problem 8
A box of 50 Newton of weight is brought by a boy from A to B and then brought back to A.
What is the work done by this boy?
Answer
W = 0 joule
(There is no displacement of the box)
Question9
A car of
mass 900 kg accelerates at 3 ms-2 from rest. How much work is done after it has
travelled 100 metres?
Worked
solution:
There are
two steps involved in solving this problem:
Step 1 : Calculate the force required to cause the acceleration.
Force = mass × acceleration
F = ma
F = 900 × 3
F = 2700 N
F = 900 × 3
F = 2700 N
Step 2 : Then use the work
equation.
W
= Fs
= 2700 × 100
= 270 000 J
= 270 kJ Ans. 270 kJ
= 2700 × 100
= 270 000 J
= 270 kJ Ans. 270 kJ
http://www.physicsclassroom.com/class/energy
POWER IS THE RATE OF DOING WORK
POWER = WORK/TIME
Unit- WATTS
1Watt = 1Joule/second
FORMS
OF POTENTIAL ENERGY
Potential Energy
|
Examples
|
Gravitational PE
|
Water stored in a dam, Any object at a
height
|
Chemical PE
|
Food and fuels
Coal,Petroleum, Battery
|
Elastic PE
|
Stretched spring, Bow and arrow
|
Nuclear PE
|
Nuclear reactors, Atom bomb
|
A ball of mass75gram is dropped from a height of
5m.Ignoring air resistance at what speed does it hit the ground?
Question 11
A stone of mass 2kg is dropped from a height of 10m. Calculate its
KE when it is 2m above the ground.
Question 12
How does the kinetic energy of a body change when the speed of the body is doubled?
A 2.5kg box slides down an incline 40m long inclined at 20˚to the horizontal.
Question 12
How does the kinetic energy of a body change when the speed of the body is doubled?
Question 13
A 2.5kg box slides down an incline 40m long inclined at 20˚to the horizontal.
a)
Represent the frictional force and weight of the box in the diagram.
b)
Calculate the height(h) lost by the box when it reaches the bottom.
c)
Calculate the potential energy lost by the box in reaching the bottom.
d)
Calculate the Kinetic energy of the box, if it moves down with a constant speed
of 2m/s.
e)
Calculate the work done against friction when the box reaches the bottom.
f)
Calculate the frictional force
Question 14
A body of mass 10kg moves down an inclined surface of length 25m.It is inclined at an angle35˚ to the horizontal.
1) State how does the PE of the mass gets converted as it moves down the inclined plane.
2)Calculate
a)the vertical height lost when the body reaches the bottom.
b) P:E lost by the body when it reaches thebottom.
c)K:E of the body if it moves down with a constant speed of 5m/s
d) work done against friction
e) frictional force
Question 14
A body of mass 10kg moves down an inclined surface of length 25m.It is inclined at an angle35˚ to the horizontal.
1) State how does the PE of the mass gets converted as it moves down the inclined plane.
2)Calculate
a)the vertical height lost when the body reaches the bottom.
b) P:E lost by the body when it reaches thebottom.
c)K:E of the body if it moves down with a constant speed of 5m/s
d) work done against friction
e) frictional force
Question15
A
box of mass 50kg is being pushed up an inclined plane of length 30m which is
inclined at an angle of θ= 25˚to the horizontal. If it takes 2min for pushing
the box up, (ignoring friction) Calculate
a)Work
done in pushing the box up
b) power out put.
Question 16
A 5kg box slides down an incline 30m long inclined at 10˚to the horizontal.
Question 16
A 5kg box slides down an incline 30m long inclined at 10˚to the horizontal.
a)
Calculate the height(h) lost by the box when it reaches the bottom.
b)
Calculate the potential energy lost by the box in reaching the bottom.
c)If work done against friction is 50J,calculate the KE of the body when it reaches the bottom .
d) calculate the velocity with which it strikes the ground
c)If work done against friction is 50J,calculate the KE of the body when it reaches the bottom .
d) calculate the velocity with which it strikes the ground
Conservation of energy in a pendulum
http://www.passmyexams.co.uk/GCSE/physics/conservation-of-energy-and-energy-transfer.html
ELASTIC AND IN- ELASTIC COLLISION
https://www.youtube.com/watch?v=Xe2r6wey26E
https://www.youtube.com/watch?v=8ko3qy9vgLQ
Elastic
collision
|
In- Elastic
collision
|
|
Total energy
|
conserved
|
conserved
|
Linear
momentum
|
conserved
|
conserved
|
Kinetic energy
|
conserved
|
NOT conserved
|
Example
|
Collision
of gas molecules, collision between billiard balls
|
Automobile
collisions
|
Question 17
Calculate the percentage efficiency if the out put of a truck is 7000J and the input is 12000J.
Question 18
Calculate the input power if the out put power is 1000W and the efficiency is 60%
Question 19
An electric motor is used to lift 0.6 kg mass through a height of 1m. The energy it uses is measured on an energy meter as 10J.Calculate the efficiency of the motor
solution.
In put energy(th energy the motor uses) =10J
out put enegy=P:E of the mass=mgh
=0.6x10x1=6J
efficiency = out putx 100/input
= 6/10 x100=60%
Question 20
Calculate the efficiency of the light bulb using the Sankey diagram
Question 21
Calculate the efficiency of the LED lamp using the Sankey diagram
Question 22
The Sankey diagram for three different types of lamps are shown in the diagram.Find out which types of lamps are most efficient
| 23. | The maximum amount of work that can be done by a 70 kW machine in 5 seconds is | |||||
| ||||||
| 24 | Kinetic energy of a body in motion equals the product of half its mass and the square of its _______ | |||||
| ||||||
| 24 | A boy throws a ball vertically upwards from ground level. If the ball reaches a maximum height of 40 m and the gravitational acceleration is 9.8 m/s2, with what speed did the boy throw the ball? | |||||
| ||||||
| 25. | By definition, work is done when a _______ moves through a distance. | |||||
| ||||||
| 26. | A mass of 2 kg is raised through a vertical distance of 90 m. If the gravitational acceleration is 9.8 m s-2, then the potential energy gained by the mass is | |||||
| ||||||
| 27. | A machine that produces 80 J of work by using 100 J of energy has an efficiency of | |||||
| ||||||
| 28. | A carton is pulled along the ground for a distance of 3 m. If the average frictional force is 61 N, then the work done is | |||||
| ||||||
Question29
A water wheel is powered by 3600kg of water
falling through a height of 5m each minute. If the power out put is 1200w what
is the efficiency of the wheel?
Out put power = 1200W
In put energy = PE lost by water falling on the wheel
PE energy lost in 1minute = mgh
= 3600x10x5
=180000J
Work done on the wheel (in put)in one minute=180000 J
Work done on the wheel (in put)in one second=180000/60s
=3000w(power in put)
Power input= 3000W
Efficiency= power O.P/power I.p
x100
= 1200 x 100/3000
= 40%
Question 30
A pump lifts 200 kg of water per minute through a vertical height of 15m Calculate a) the out put power b)Input power if the efficiency is 65%
PE gained when 200kg of water is lifted= mgh
= 200x 10x 15=30000J
power out put= 30000/60 = 500W
I.N power = O.P x 100/efficiency
1.Define the
following
a.work done
b.energy
c.power
d.Potential energy
e.Kinetic energy
f. 1joule
g.1 watt
2. Write the
different units of
a. work done
b. energy
c. power
3.
A
force acts on a box and displaces it through 15m in a horizontal surface.
The work done by the force on the block is 30 joule. Find the magnitude of the
force.
4. A boy lifts up a book from
the floor to the table. The mass of the book is 0.5kg and the height of the
table is 80 cm. Find the work done by the boy when the acceleration due to
gravity is 10 m/s2
5.The energy dissipated by a lamp is 3000 joule in 3min
Find the power of the lamp.
6. A ball of mass 2kg is dropped from a height of 10m.Ignoring air
resistance calculate at what speed does it hit the ground?7. How does the kinetic energy of a body change when the speed of the body is tripled?
8. The Kinetic energy of a body is 12J .What will be its new kinetic energy if the velocity of the body is doubled?
9. A 5kg box slides down an incline 5m long inclined at 25˚to the horizontal.
a) Calculate the height(h) lost by the box when it
reaches the bottom.
b) Calculate the potential energy lost by the box
in reaching the bottom.
c) Calculate the Kinetic energy of the box, if it
moves down with a constant speed of 1m/s.
d) Calculate the work done against friction when the
box reaches the bottom.
e)
Calculate the frictional force.
10.A body of
mass 50kg is dropped from the top of a
tower of height 100m.Calculate
a) the potential energy of the body when it is on
top.
b) the kinetic energy with which it strikes
the ground.
c) velocity of the
stone when it strikes the ground
11. Calculate the input power if the out put power is 1000W and the efficiency is 40%
1.Define the
following
a.work done
b.energy
c.power
d.Potential energy
e.Kinetic energy
f. 1joule
g.1 watt
2. Write the
different units of
a. work done
b. energy
c. power
3.
A
force acts on a box and displaces it through 15m in a horizontal surface.
The work done by the force on the block is 30 joule. Find the magnitude of the
force.
4. A boy lifts up a book from
the floor to the table. The mass of the book is 0.5kg and the height of the
table is 80 cm. Find the work done by the boy when the acceleration due to
gravity is 10 m/s2
5.The energy dissipated by a lamp is 3000 joule in 3min
Find the power of the lamp.
6. A ball of mass 2kg is dropped from a height of 10m.Ignoring air resistance calculate at what speed does it hit the ground?
7. How does the kinetic energy of a body change when the speed of the body is tripled?
8. The Kinetic energy of a body is 12J .What will be its new kinetic energy if the velocity of the body is doubled?
9. A 5kg box slides down an incline 5m long inclined at 25˚to the horizontal.
a) Calculate the height(h) lost by the box when it
reaches the bottom.
b) Calculate the potential energy lost by the box
in reaching the bottom.
c) Calculate the Kinetic energy of the box, if it
moves down with a constant speed of 1m/s.
d) Calculate the work done against friction when the
box reaches the bottom.
e)
Calculate the frictional force.
10.A body of
mass 50kg is dropped from the top of a
tower of height 100m.Calculate
a) the potential energy of the body when it is on
top.
b) the kinetic energy with which it strikes
the ground.
c) velocity of the
stone when it strikes the ground
11. Calculate the input power if the out put power is 1000W and the efficiency is 40%
www.physicsclassroom.com/class/energy
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