Everything Science Grade 11

12.3 CHAPTER 12. FORCE,MOMENTUM AND IMPULSE

Example 23: Equilibrium

QUESTION

A car engine of weight 2000 N is lifted by means of a chain and pulley system. The engine is

initially suspended by the chain, hanging stationary. Then, the engine ispulled sideways by a

mechanic, using a rope. The engine is held insuch a position that thechain makes an angle

of 30 ◦with the vertical. In thequestions that follow, the masses of the chain and the rope can

be ignored.

chain

engine

initial

30 ◦

chain

rope

engine

final

1. Draw a free body representing the forces acting on the engine in theinitial situation.


2. Determine the tension in the chain initially.


3. Draw a free body diagram representing the forces acting on the engine in the final situa-
   tion.


4. Determine the magnitude of the applied force and the tension in the chain in the final
   situations.

SOLUTION

Step 1 : Initial free body diagram for the engine

There are only two forces acting on the engine initially: the tension in thechain,

Tchainand the weight of the engine, Fg.

�

Tchain

Fg

Step 2 : Determine the tensionin the chain

The engine is initially stationary, which meansthat the resultant forceon the

engine is zero. There arealso no moments of force. Thus the tension in the chain