Power Calculating Power Work, energy and Power

1. POWER

2. POWER
• It is the rate of doing work or the
rate of using energy.
*Doing work at a faster rate requires
more power. To increase power, you
can increase the amount of work
done in a given time, or you can do a
given amount of work in less time.

3. CALCULATING POWER
P =
𝑾
𝒕
Where:
P = Power
W = Work
t = time

4. UNITS OF POWER
1 J/s = 1 Watt
1 Kilowatt (KW)= 1000 W
1 horsepower (hp) = 746 W
hp – unit of power of engines and
machines.
KW – used for electrical power.

5. Problem
You exert a vertical force of
72 N to lift a box to a height of 1.0
m in a time of 2.0 seconds. How
much power is used to lift the
box?

6. Solution
Given: F = 72 N
h = 1.0 m
t = 2.0 s
P= ?
P = W/t P= 72 N ( 1.0 m)/2.0 s
W = Fd = 72 J/2.0 s
P = Fd/t = 36 J/s or 36 W

7. Seat work
1. A 60-kg jogger runs up a long flight
of stairs in 4.0s. The vertical height of
the stairs is 4.5 m. Estimate the
jogger’s power output in watts and
horsepower.
2. How long will it take a 2760 W motor
to lift a 385-kg piano to a sixth-story
window 16.0 m above?
3. Your family is moving to a new
apartment. While lifting a box 1.5 m
straight up to put it on a truck, you
exert an upward force of 200 N for