Download Answer Energy Test Day 10

Energy Test
Name ___________________________________
Hour ___________
Level 2
1. Give an example in which the electrical energy changes to thermal energy.
Electric powered portable heater
2. Give an example in which the electrical energy changes to kinetic energy.
A motor running.
3. When a pole-vaulter flexes the pole, the pole-vaulter increases the pole’s elastic potential energy
to increase the pole-vaulter’s initial potential energy.
4. Which one is equal to mechanical energy?
A. Chemical energy plus its nuclear energy.
B. Thermal energy plus electrical energy.
C. Kinetic energy plus potential energy.
D. Thermal energy plus kinetic energy.
5. What is the work done on a 2 newton mass when it is lifted to a height of 3 meters?
A. 60 joule.
B. 6 joule.
C. 6 newton.
D. 5 newton.
6. What is the gravitational potential energy of a 4 kilograms rock sitting on a cliff of height 40
meters?
A. 1568 joule.
B. 160 joule.
C. 40 joule.
D. 10 joule.
7. What is the System of International ‘SI’ unit of power?
A. newton-meter.
B. newton.
C. joule.
D. watt.
8. What is a drawback of solar energy?
A. It cannot be converted directly into electrical energy.
B. It is not a renewable resource.
C. It produces water pollution.
D. It depends on the climate.
9. Which statements is true in context of power?
A. To increase power, you can decrease the amount of work you do in a given amount of time,
or you can do a given amount of work in less time.
B. To increase power, you can decrease the amount of work you do in a given amount of time,
or you can do a given amount of work in more time.
C. To increase power, you can increase the amount of work you do in a given amount of time,
or you can do a given amount of work in less time.
D. To increase power, you can increase the amount of work you do in a given amount of time,
or you can do a given amount of work in more time.
10. A small 10 kilogram canoe is floating downriver at a speed of 2 m/s. What is the canoe’s kinetic
energy?
A. 40 joule
B. 20 joule
C. 10 joule
D. 5 joule
11. A 7 kilograms sled is moving at a speed of 3 meter per seconds. What is the sled’s kinetic energy?
Kinetic energy = ½ m*v² = 0.5 × 7 × 32 = 31.5 joule
12. What are some ways of conserving energy at home?
Turn the lights off when you are leaving.
13. Nuclear power plants are designed to convert nuclear energy into what type of energy?
Electrical energy
14. What are the variables on which the gravitational potential energy of an object depends?
Mass, gravity, and height.
15. What energy conversion takes place as an arrow is shot from a bow?
Elastic potential energy changes to kinetic energy.
16. Fill the box with one of the terms given with the chart.
Amount of work
(More, Less, Same, or no work)
When holding a book
same
in their hands?
When pushing hard
no
against a brick wall?
work
When walking up the
more
stairs?
Is the person doing work?
(yes or No)
When holding a book in no
their hands?
When pushing hard
yes
against a brick wall?
When walking up the
yes
stairs?
Power
(more or Less)
You take the same
amount of time to do
more work.
Same distance; same
time; more force.
more
less
Level 3
1. A bicycle and rider with a combined mass of 150 kilograms have 1200 joule of kinetic energy
while coasting. What is the speed of the bicycle?
A. 120 meter per second.
B. 60 meter per second.
C. 8 meter per second.
D. 4 meter per second.
2. Why is the gravitational potential energy of an object one meter above the moon’s surface less
than its potential energy one meter above Earth’s surface?
Earth’s gravity is greater than the moon’s gravity.
3. Two blocks are released from the top of a building. One falls straight down while the other slides
down a smooth ramp. If all friction is ignored, which one is moving faster when it reaches the
bottom?
Both will reach at the same speed. Since their height is same, the total energy at the top will be
equal to total energy at the bottom.
4. Show that the unit kilogram squared meter per squared second “kg.m2/s2”, calculated from the
potential energy equation, is equivalent to a joule.
Potential energy = m g h
m = mass = unit is ‘kg’
g = gravity = unit is m/s2
h = height = unit is ‘m’
Potential energy = m g h = kg × m/s2 × m = kg.m2/s2
The SI unit of potential energy is joule and unit of potential energy is also kg.m2/s2 so they are
equivalent to each other.
5. Between what location does the
kinetic energy of the pendulum bob
increases the most?
A. B and D
B. A and B.
C. A and C.
D. C and D.
6. How is work done when you lift a
book?
Work is the product of displacement and force. When you lift a book, there is a displacement in the
direction or in opposite direction of the gravitational force. So there is a work done.
7. If two swimmers compete in race, does the faster swimmer develop more power?
Yes, power is equal to work divided by time, so less the time more the power.
8. Compare the gravitational potential energy of the ball at locations B and E shown in figure. Explain
your answer.
B has some potential energy as its heading for the floor.
At C there is no potential energy but all kinetic energy.
From C the ball’s kinetic energy start changing to
potential energy as it rises. At D it has all potential
energy higher than B. The ball falls again which in turn
loss its potential energy and at E it has potential energy
less than D.
9. A 60 grams golf ball fall from a height of 3 meters. It rebounds to 1.5 meters. How much energy is
lost?
Potential energy lost = m g h = 0.060 × 9.8 × 1.5 = 0.882 joule
Level 4
1. The kinetic energy of an object is 40 joules. If the mass and speed of the ball is doubled, what will be
the kinetic energy of the object? Calculate the change in the kinetic energy.
Kinetic energy = ½ m*v²
= 2 × 22 {mass is doubled means 2 and speed is doubled means 2}
=2×4
= 8 times = 40 × 8 = 320 joule
2. A 10 kilograms cart is moving at a speed of 3 meter per second. At what speed will the cart have
twice as much kinetic energy?
Kinetic energy = ½ m*v²
= 0.5 × 10 × 32 = 45 joule
Double the kinetic energy = 2 × 45 = 90 joule
Kinetic energy = ½ m*v²
90 = 0.5 × 10 × v2
90 = 5 v2
v2 = 90 ÷ 5
v2 = 18
v = 4.24 m/s