Download Review for Chapter 5 and 6 Test

Review for Chapter 5
Concepts:
1. Know the definition for work and the equations to solve for work.
2. Be able to give examples of mechanical work and examples of when work is NOT
being done.
3. Be able to define gravitational potential energy and kinetic energy and give
examples.
4. Understand the principle of conservation of energy.
5. Formulas that will be given to you:
a. PE=mgh (Remember it can be called GPE also)
b. KE=1/2mv2
c. W=Fdcosθ (if there is no angle(θ), than θ is 0)
d. P=W/t
e. ME=KE+PE
f. PEi+KE=PEf+KEf
Problems:
1.
A man pushes a broken-down car off to the side of the road. If he pushes it 3.0 m
with a force of 100N, what work was done on the car by the man?
W=f×d 100N×3.0m= 300J
2.
A 5.75 kg rock falls from a height of 7.25 m. Just before it hits the ground, what
will its kinetic energy be? What will it’s speed be?
5.75kg×10m/s²×7.25m = 417J PE
3.
KE
417J = 5.75v²/2
v=12
What is the kinetic energy of a 1500 kg airplane moving at 200.0 m/s?
KE= mv²/2
1500(200²)/2 = 30000000J
4. The graphic below shows a pendulum swinging back and forth. If the ball
has a mass of 10kg and is swinging on a 10m long rope, what is it’s
mechanical, potential, and kinetic energy at all 5 locations? (The angle between 1 and 3
is 30 degrees. The angle between 2 and 3 is 18 degrees. There is no friction present.)
OMIT
Most PE
Most KE
6. Calculate the potential energy, kinetic energy, mechanical energy, velocity, and height
of the skater at the various locations. (No friction present)
1: PE= 0
KE= 1920
ME= 1920
2: PE= 600
KE=1370
ME=1920
V= 6.6
3: PE= 1920
KE=0
ME- 1920
V=0
H=3.2
7. An escalator is used to move 20 passengers every 60s from the first floor of a
department store to the second. The second floor is located 5 meters above the first floor.
The average passenger's mass is 54.9 kg. Determine the power requirement of the
escalator in order to move this number of passengers in this amount of time.
W=f×d convert kg to N: 54.9kg×10=549N 549N×5m=2745J p=w/t 2745J/60s=
45.75W
8. An escalator is used to move 10 passengers every 60s from the first floor of a
department store to the second. The second floor is located 8 meters above the first floor.
The average passenger's mass is 65 kg. Determine the power requirement of the escalator
in order to move this number of passengers in this amount of time.
650N×8m=5200J 5200J/60s=86.7W
9. Two physics students, Will N.Andable and Ben Pumpiniron, are in the weightlifting
room. Will lifts the 100-pound barbell over his head 10 times in one minute; Ben lifts the
100-pound barbell over his head 10 times in 10 seconds. Which student does the most
work? __Same_Why? As long as they are the same hieght and are moving the same
mass they are doing the same amount of work.
Which student has the most power output? __Ben___Why? He was faster
10. When is work being done? When a mass is being displaced.
11. What is inertia based on? MASS!
12. What would the graph of PE vs time look like for an object falling downwards and
hitting the ground? (Draw it)
13. What would the graph of KE vs time look like for an object falling downwards and
hitting the ground?
14. What would the graph of ME vs time look like for an object falling downwards and
hitting the ground?
15. If you are given kg, and the formula calls for Force, what do you do? ×9.8
16. Where in the diagram below would it have the most potential energy? 1
17. Where in the diagram below would the coaster be going the fastest? 2
Position
PE
KE
ME
v
1
3500
0
3500
0
2
0
3500
3500
26.5
3
2800
700
3500
11.8
4
1500
2000
3500
20
18. What happens to the kinetic energy as something falls? increase
19. What happens to the potential energy as something falls? decrease
20. What happens to the mechanical energy as something falls? stays the same
21. What happens to an objects acceleration as it falls? Stays the same
22. Is energy a scalar or a vector? Scalar
23. Is weight a force or a mass measurement? Force
24. What is the only way to increase an objects falling velocity before it hits the ground?
(neglecting friction) Increase height
25. If you hit a baseball into the air, what happens to the kinetic energy you give it? It decreases
as it rises up and increases as the ball fall back down.
26. In real life, every single energy conversion turns some of the energy into __Thermal
energy_____ because of __Conservation of energy___.
27. To get the cart in the picture below to move 8m, how much work do you have to do to it?
W=f×d 6kg×10=60N
W=60N×8m=480J
28. What happens to KE when you triple your velocity? What happens when you triple your
mass? Velocity:3², mass triples