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Three blocks of masses $m_1 = 2\text{ kg}$, $m_2 = 3\text{ kg}$ and $m_3 = 5\text{ kg}$ are placed on a horizontal frictionless surface and a force of 30N pulls the system as shown below. The value of tension in the string between $m_2$ and $m_3$ will be

This question was previously asked in
WBJEE 2026 Physics and Chemistry Question Paper (24-May-2026)
The correct answer is
$15\text{ N}$

To find the tension in the string between blocks \(m_2\) and \(m_3\), we need to analyze the forces acting on the blocks and utilize Newton's second law of motion.

First, calculate the total mass of the system:

\(m_{\text{total}} = m_1 + m_2 + m_3 = 2\,\text{kg} + 3\,\text{kg} + 5\,\text{kg} = 10\,\text{kg}\)

Now, calculate the acceleration of the system using the force applied:

\(F = 30\,\text{N}\)

Using Newton's second law \(F = m \cdot a\),

\(a = \frac{F}{m_{\text{total}}} = \frac{30\,\text{N}}{10\,\text{kg}} = 3\,\text{m/s}^2\)

To find the tension \(T\) in the string between \(m_2\) and \(m_3\), consider only the mass \(m_3\). The only force causing its acceleration is the tension in the string:

Using \(T = m_3 \cdot a\),

\(T = 5\,\text{kg} \cdot 3\,\text{m/s}^2 = 15\,\text{N}\)

Thus, the tension in the string between \(m_2\) and \(m_3\) is \(15\,\text{N}\).

The correct answer is: \(15\,\text{N}\)

Diagram of the blocks and force applied
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