Everything Science Grade 11

CHAPTER 12. FORCE,MOMENTUM AND IMPULSE 12.3

exactly balances the weight of the engine. The tension in the chain is:

Tchain = Fg

= 2000N

Step 3 : Final free body diagramfor the engine

There are three forces acting on the engine finally: The tension in the chain, the

applied force and the weight of the engine.

Fapplied

Tchain

Fg

30 ◦

30 ◦

Step 4 : Calculate the magnitude of the applied forceand the tension in thechain in

the final situation

Since no method was specified let us calculatethe magnitudes algebraically.

Since the triangle formed by the three forces is aright-angle triangle thisis easily

done:

Fapplied

Fg

= tan30◦

Fapplied = (2000N)tan30◦

= 1155N

and

Tchain

Fg

=

1

cos30◦

Tchain =

2000N

cos30◦

= 2309N

Exercise 12 - 5

1. The diagram shows an object of weight W, attached to a string. A horizontal force F is applied
   to the object so that thestring makes an angle of θ with the vertical whenthe object is at rest.
   The force exerted by thestring is T. Which one of the following expressions is incorrect?

(a) F + T + W = 0

(b) W = T cos θ

(c) tan θ =WF

(d) W = T sin θ