Power is defined as the rate of doing work or using energy. It can be calculated by dividing the amount of work done by the time taken to do that work. Common units of power include watts (W), kilowatts (kW), and horsepower (hp). In the example, a box is lifted 1 meter by a force of 72 newtons over 2 seconds. Calculating power as work over time gives 36 watts, the amount of power used to lift the box.

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