Question

Two masses 5 kg and 3 kg are suspended from the ends of an inextensible light string passing over a frictionless pulley. When the masses are released, force exerted by the string on the pulley is :

• A. $8N$
• B. $2N$
• C. $5N$
• D. $65N$

Answer 1

The correct option is C $5N$

Ref .Image.

force causing motion = Driving force - opposing force

for block A,

5a = 50-T

for block B, 3a = T - 30

___________________

8a = 20

$\therefore a=2.5m/s^2$

$\therefore T=37.5N\leftarrow$ This is tension.

$\therefore$ force on pulley is

(80-75) = 5 N downward

$\uparrow$

Total weight