Transcript Power

Topic
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Displacement
Vectors
Kinematics
Graphs
Energy
Power
Springs
Shadows
Field of Vision
Colors
Concave mirrors
Convex mirrors
Refraction
Lenses
Optical Power
Slides Minutes
9
27
13
39
13
39
10
30
10
30
5
15
4
12
3
9
7
21
3
9
7
21
4
12
5
15
10
30
6
18
Power is the rate of doing work. It tells us how fast work
is being done. Power is important in order to establish
the “speed” with which a given force acts.
The formula for power is:
Velocity
Where: P = power in watts (W)
F = force in newtons (N)
t = time in seconds (s)
v = velocity in m/s
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Power Slide:
6. 1
A 20 kg object is pushed 15 m along a horizontal frictionless
surface by a horizontal force of 8 N. If the work was done in
a time of 12 s, calculate:
a) The work done.
b) The power output.
120 J
10 W
c) What becomes of the work done?
It is lost to overcome friction
(in the form of heat and sound)
Note that we assume the object is moved at constant velocity.
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Power Slide:
6. 2
What power is required to raise a mass of 40 kg a distance
of 5 m in a time of 2 s?
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Power Slide:
6. 3
A 2 000 kg elevator is raised a distance of 18 m in a time of 40 s.
Determine:
a) The work done.
3.6 x 105 J
b) The rate of doing work.
9 x 103 W
c) What becomes of the work done?
It is gained by the elevator in the form of potential energy.
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Power Slide:
6. 4
If 700 W of power is needed to keep a boat moving through water
at a constant speed of 10 m/s, what is the magnitude of the force
exerted by the motor of the boat?
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Power Slide:
6. 5
Betty uses the hoist illustrated on the right
to raise a mass of 200 kg.
If she can pull the rope 5.0 metres in a time
of 10 seconds, what is Betty’s power output?
Note: Disregard friction.
A) 17.0 W
I.M.A. = 6 (6 ropes)
B) 100 W
C) 163 W
D) 980 W
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… and good luck!