2. the amount of energy transferred or converted per unit
time.
Or the rate of doing work
The SI unit is joule/second or also called as watt (W)
Named after Scottish inventor JAMES WATT (1736-1819)
Another unit is horsepower or hp which is equal to 746 W
3. • Great power (powerful) means a large amount of work or
energy developed in a short time.
• Examples:
1. when a powerful car accelerates rapidly, it does a large amount of
work and consumes a large amount of fuel in a short time.
2. Climbing a stairs in a short period of time among other people.
4. P = W/t
W= Fd therefore; P = Fd/t
P = power F = force
W = work d = distance/displacement
T = time
5. 1. A garage hoist lifts a truck up 2 meters above the ground in 15 seconds. Find
the power delivered to the truck. [Given: 1000 kg as the mass of the truck]
First we need to calculate the work done, which requires the force necessary to
lift the truck against gravity:
F = mg = 1000 x 9.81 = 9810 N.
W = Fd = 9810N x 2m = 19620 Nm = 19620 J.
The power is P = W/t = 19620J / 15s = 1308 J/s = 1308 W. P=f.v
6. 2. To lift a baby from a crib, 50 J of work is done. How
much power is required to lift the baby in 0.5 s?
• Given:
W = 50 J; t = 0.5 s; P = ?
• Solution: P = W / t
= 50 J / 0.5 s
= 100 J/s or 100 W
• Answer: The power needed is 100 W in order to lift a baby in 0.5 seconds.
7. Solve the following problems.
1. A force of 75 N is exerted on a 45 kg sofa, and the sofa is moved 5 m.
How much work is done moving the sofa?
2. A lawn mower is pushed with a force of 80 N. if 12,000 J of work is
done in mowing a lawn, what is the total distance the lawn mower was
pushed?
