Download Answer Review Worksheet Day 9

Test Review # Day 9
Name _____KEY_____________________
Hour ___________
1. Give an example in which the electrical energy changes to sound energy.
IPod playing music
2. Give an example in which the kinetic energy changes to potential energy.
Ball rolling up the hill.
3. When a pole-vaulter flexes the pole, the pole-vaulter increases the pole’s elastic potential
energy.
4. When a pole-vaulter flexes the pole, the pole-vaulter increases the pole’s elastic potential
energy and transforms it to increase the pole-vaulter’s gravitational potential energy.
5. 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.
6. What are some ways of conserving energy at home?
Turning off lights when you are leaving.
7. Nuclear power plants are designed to convert nuclear energy into what type of energy?
Electrical energy
8. What are the variables on which the gravitational potential energy of an object depends?
The mass, gravity, and height.
9. Show that the unit “kg.m2/s2”, calculated from the kinetic energy equation, is equivalent to
a joule.
Kg=Mass=m
m²/s²= Velocity squared=v ²
Kinetic energy = ½ mass * velocity² = ½ m*v²
kg.m2/s2 = ½ m*v²= kinetic energy
Kinetic energy is also joule so,
joule= kg.m2/s2
10. What energy conversion takes place as an arrow is shot from a bow?
Elastic potential energy to kinetic energy.
11. A 7 kg sled is moving at a speed of 3 m/s. What is the sled’s kinetic energy?
Kinetic energy = ½ m*v²
= 31.5 J
12. Fill the chart with one of the word given for each category.
Amount of work
(More, Less, or Same)
When pushing a 1000
N car 20 meters?
When lifting a rock off
the ground?
Is the person doing work?
(yes or No)
more When pushing a 1000
yes
N car 20 meters?
more When lifting a rock off yes
the ground?
Power
(more or Less)
An engine can lift an
object faster.
Someone takes more
time to push a car.
more
less
Level 3
13. A 10 kg heavy rock piece falls from a 50 m tall mountain. Just before hitting the ground,
what will be its kinetic energy?
Change in potential energy = Change in kinetic energy
m g h = Change in kinetic energy
10 × 9.8 × 50 = 4900 J
14. What is the minimum amount of energy required for an 80 kg climber carrying a 20 kg pack
to climb Mt. Everest, 8850 m high?
Potential energy = m g h
= (80 + 20) × 9.8 × 8850 = 8,673,000 joule
15. A 60 grams golf ball falls from a height of 3 m. It rebounds to 1.5 m. How much energy is
lost?
Half, since the height reduced to half when it rebounds.
16. The kinetic energy of an object is 40 joules. If the mass of the ball is doubled, what will be the
kinetic energy of the object? Calculate the change in the kinetic energy.
Kinetic energy and mass are directly proportional so double the mass means double th
kinetic energy that is 80J
Level 4
17. An 11 kg sled is moving at a speed of 2.5 m/s. At what speed will the sled have twice as much
kinetic energy?
Kinetic energy = ½ m*v²
= 0.5 × 11 × 2.52 = 34.375 joule
Double the kinetic energy = 2 × 34.375 = 68.75 joule
Kinetic energy = ½ m*v²
68.75 = 0.5 × 11 × v2
68.75 = 5.5v2
v2 = 68.75 ÷ 5.5
v2 = 12.5
v = 3.53 m/s
18. A rock is thrown straight up with an initial velocity of 15.0 m/s. Ignore energy lost to air
friction. How high will the rock rise?
Change in kinetic energy = Change in potential energy
½ m*v² = m g h
0.5 ×m × 152 = m × 9.8 ×h
112.5 m = 9.8 m h
Dividing by ‘m’ on both sides will cancel out the m, and we get,
h = 112.5 ÷ 9.8 = 11.47 m
19. A pole-vaulter clears 6.00 m. With what speed does he strike the mat in the landing area?
Change in potential energy = Change in kinetic energy
m g h = Change in kinetic energy
m × 9.8 × 6 = ½ m*v²
Dividing by ‘m’ on both sides will cancel out the m, and we get,
58.8 = ½ v²
v² = 58.8 × 2 = 117.6
Taking square root on both the sides we get,
V = 10.8 m/s
20. A bobsled makes a run down an ice track starting at 150 m vertical distance up the hill. If
there is no friction, what is the velocity at the bottom of the hill?
Change in potential energy = Change in kinetic energy
m g h = Change in kinetic energy
m × 9.8 × 150 = ½ m*v²
Dividing by ‘m’ on both sides will cancel out the m, and we get,
1470 = ½ v²
v² = 1470 × 2 = 2940
Taking square root on both the sides we get,
V = 54.22 m/s