question_answer

A pulley system with frictionless massless puller and ideal string is used to lift a weight of 100 N. F is the force that is sufficient to lift the load.

Now, choose the correct option.

A) F is at least 25 N

B) F is almost 25 N

C) F is exactly 25 N

D) Load cannot be lifted by given arrangement

Correct Answer: A

Solution :

Tensions involved are as shown below.

For equilibrium of pulley 2,

\[\Rightarrow \]\[F={{T}_{1}}\]

\[\Rightarrow \]\[{{T}_{2}}-{{T}_{1}}-F=0\]

\[\Rightarrow \]\[{{T}_{2}}=2F\]

For equilibrium of pulley 3,

\[\Rightarrow \]\[{{T}_{1}}+{{T}_{1}}+{{T}_{2}}-W=0\]

\[\Rightarrow \]\[4F=W,F=25N\]

To lift the load F is atleast 25 N is required.