Everything Science Grade 12

CHAPTER 8. WORK, ENERGY AND POWER 8.2

applied force parallel tothe ground is

F|| = F· cos(60◦)

= 10 N· cos(60◦)

= 5 N

Step 4 : Substitute and calculate the work done

Now we can calculate the work done on the box:

W = F�s

= (5 N)(5 m)

= 25 J

Note that the answer ispositive as the component of the force F�

is in the same directionas the motion.

Exercise 8 - 1

1. A 10 N force is applied to push a block across a friction free surface for a dis-
   placement of 5.0 m to the right. The block hasa weight of 20 N. Determine the
   work done by the following forces: normal force, weight, applied force.
   N

Fg

Fapp

2. A 10 N frictional force slows a moving blockto a stop after a displacement of 5.0
   m to the right. The block has a weight of 20 N.Determine the work done by the
   following forces: normal force, weight, frictional force.
   N

Fg

Ffriction

3. A 10 N force is applied to push a block across a frictional surfaceat constant
   speed for a displacement of 5.0 m to the right.The block has a weightof 20 N
   and the frictional force is10 N. Determine the work done by the followingforces:
   normal force, weight, frictional force.
   N

Fg

Ffriction Fapp