Everything Science Grade 12

8.4 CHAPTER 8. WORK, ENERGY AND POWER

A

B

C

v

h

Calculate the speed ofthe pendulum when itreaches point B (the equilibrium

point). Assume that there are no external forcesacting on the pendulum.

More practice video solutions or help at http://www.everythingscience.co.za

(1.) 01tw (2.) 01tx (3.) 01ty

8.4 Power ESCEG

Now that we understand the relationship between work and energy, we are ready to

look at a quantity thatdefines how long it takes for a certain amountof work to be

done. For example, a mother pushing a trolley full of groceries can take30 s or 60 s to

push the trolley down anaisle. She does the sameamount of work, but takes a different

length of time. We use the idea of power to describe the rate at which work is done.

FACT

The unit watt is named
after Scottish inventor
and engineer James Watt
(19 January 1736 - 19
August 1819) whose im-
provements to the steam
engine were fundamen-
tal to the Industrial Rev-
olution. A key feature of
it was that it brought the
engine out of the remote
coal fields into factories. DEFINITION: Power

Power is defined as therate at which work is done or the rate at which

energy is expended. Themathematical definitionfor power is:

P = F· v (8.3)

(8.3) is easily derived from the definition of work. We know that:

W = F· d.