Question

A $4\text{kg}$ block is on a smooth horizontal table. The block is connected to a second block of mass $1\text{kg}$ by a massless flexible taught cord that passes over a frictionless pulley. The $1\text{kg}$ block is $1\text{m}$ above the floor. The two blocks are released from rest. With what speed (in $\text{m/s}$) does the $1\text{kg}$ block hit the ground?

• A. $3\text{m/s}$
• B. $4\text{m/s}$
• C. $2\text{m/s}$
• D. $5\text{m/s}$

Answer 1

The correct option is C $2\text{m/s}$

By the law of mechanical energy conservation
Decrease in potential energy of $1\text{kg}$
= increase in kinetic energy of both
$\therefore 1\times 10\times 1=\frac{1}{2}(4+1)v^2$
(velocity will be same as they are connected by string )
$v=2\text{m/s}$