Everything Science Grade 12

8.2 CHAPTER 8. WORK, ENERGY AND POWER

Example 1: Calculating Work Done I

QUESTION

If you push a box 20 mforward by applying a force of 15 N in the forward

direction, what is the work you have done on the box?

SOLUTION

Step 1 : Analyse the question todetermine what information is provided

• The force applied is F=15 N.


• The distance moved is s=20 m.


• The applied force anddistance moved are inthe same
  direction. Therefore, F�=15 N.

These quantities are allin the correct units, so no unit conver-

sions are required.

Step 2 : Analyse the question todetermine what is beingasked

• We are asked to find the work done on the box.We know
  from the definition thatwork done is W = F�s

Step 3 : Next we substitute thevalues and calculate thework done

W = F�s

= (15 N)(20 m)

= 300 J

Remember that the answer must be positive as the applied

force and the motion are in the same direction(forwards). In this

case, you (the pusher) lose energy, while the boxgains energy.

Example 2: Calculating Work Done II

QUESTION

What is the work doneby you on a car, if youtry to push the car up ahill by