Question

At certain moment of time, velocities of 1 and 2 both are $1m/s$ upwards. Find the velocity of 3 at that moment.

• A. $-3m/s$ downwards
• B. $-2m/s$ downwards
• C. $1m/s$ upwards
• D. $3m/s$ upwards

Answer 1

The correct option is A $-3m/s$ downwards

Let velocity of block 3 be $v$

Draw F.B.D. in order to evaluate T in each string.

Now , suppose velocity of block 3 be in upward direction.

Using constraint equations,

T/2.$v$ + T/2.$v_2$ + T.$v_1$ = 0

$v$ + $v_2$ + 2$v_1$ = 0

$v$ = -3(1 m/s) {since, $v_1=v_2=1m/s$}

$v$ = $-3m/sec$