Question

Three blocks $\text{a, b and c}$ of masses $10kg$, $10kg$ and $20kg$ respectively are arranged as shown in figure. All the surfaces are frictionless and string is inextensible. A constant force $F=20N$ is applied on block $\text{a}$ as shown. Pulley and string are light. Part of the string connecting both pulleys is vertical and part of the strings connecting pulleys with masses a and b are horizontal. Choose the correct option(s) for the given system.

• A. Acceleration of block b is $0.5m/s^2$
• B. Acceleration of block $\text{b}$ is $1m/s^2$
• C. Tension in the string is $10N$
• D. Acceleration of block $\text{c}$ is $0.5m/s^2$

Answer 1

Answer: (B), (C)

The correct options are
B Acceleration of block $\text{b}$ is $1m/s^2$
C Tension in the string is $10N$

Block $\text{c}$ will remain stationary because external forces on it balance each other. Hence block $\text{c}$ won't accelerate.

Due to string constraint,
Acceleration of $\text{a}$ = acceleration of $\text{b}$
$=\frac{F}{m_a+m_b}=\frac{20}{10+10}=1m/s^2$
Tension, $T=m_b\times$ (acceleration of b)
$T=\left(10\right)\left(1\right)=10N$