Question

A $50kg$ person stands on a $25kg$ platform. He pulls on the rope which is attached to the platform via the frictionless pulleys as shown in the figure. The platform moves upward at a steady rate if the force with which the person pulls the rope is:

• A. $25N$
• B. $250N$
• C. $50N$
• D. $500N$

Answer 1

The correct option is B $250N$

Draw FBD for man and platform.

Find tension in the string.


As platform and man moving at steady rate so acceleration of both will be zero,
From FBD of platform, $2T=N+25g$

$2T-N=25g\dots \left(i\right)$
From FBD of man,$N+T=50g\dots \left(ii\right)$

By adding equation $\left(i\right)$ and $\left(ii\right)$, we get
$3T=750$
$T=250N$

Final answer :$\left(b\right)$