Everything Science Grade 12

8.3 CHAPTER 8. WORK, ENERGY AND POWER

1. Calculate the workdone by the hammer, W 1 , when
   dropped from h 1 using:

W 1 = Fg· h 1.

2. Calculate the workdone by the hammer, W 2 , when
   dropped from h 2 using:

W 2 = Fg· h 2.

3. Compare W 1 and W 2


4. Calculate potential energy at h 1 and h 2 and compare us-
   ing:
   PE = m· g· h. (8.2)

Step 3 : Calculate W 1

W 1 = Fg· h 1

= m· g· h 1

= (2 kg)(9.8 m· s−^2 )(10 m)

= 196 J

Step 4 : Calculate W 2

W 2 = Fg· h 2

= m· g· h 2

= (2 kg)(9.8 m· s−^2 )(5 m)

= 98 J

Step 5 : Compare W 1 and W 2

We have W 1 =196 J and W 2 =98 J. W 1 > W 2 as required.

Step 6 : Calculate potential energy

From 8.2, we see that:

PE = m· g· h

= Fg· h

= W

This means that the potential energy is equal tothe work done.

Therefore, PE 1 > PE 2 , because W 1 > W 2.

This leads us to the work-energy theorem.