Physics

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Physics
Review
Topic Topic Slides Minutes
1 Displacement 9 27
2 Vectors 13 39
3 Kinematics 13 39
4 Graphs 10 30
5 Energy 10 30
6 5 15
7 Springs 4 12
8 Shadows 3 9
9 Field of Vision 7 21
10 Colors 3 9
11 Concave mirrors 7 21
12 Convex mirrors 4 12
13 Refraction 5 15
14 Lenses 10 30
15 Optical Power 6 18
Power
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Power
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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PRACTICE
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6. 1
Power Slide
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
120 J
a)
The work done.
10 W
b)
The power output.
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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6. 2
Power Slide
What power is required to raise a mass of 40 kg a
distance of 5 m in a time of 2 s?
Answer
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6. 3
Power Slide
A 2 000 kg elevator is raised a distance of 18 m
in a time of 40 s. Determine
3.6 x 105 J
a)
The work done.
9 x 103 W
b)
The rate of doing work.
c)
What becomes of the work done?
It is gained by the elevator in the form of
potential energy.
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6. 4
Power Slide
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?
Answer
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6. 5
Power Slide
Betty uses the hoist illustrated on the rightto
raise a mass of 200 kg. If she can pull the rope
5.0 metres in a timeof 10 seconds, what is
Bettys power output? Note Disregard friction.
A) 17.0 W
B) 100 W
C) 163 W
D) 980 W
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The
End
and good luck!