Question

Two bodies (A and B) of masses 7 kg and 3 kg are attached to each other in the following way. If a force of 100 N is applied on A along the x direction, the force on A on B will be

• A. 10 N
• B. 20 N
• C. 30 N
• D. 9.8 N

Hint:

When calculating forces in a system with multiple objects, first find the acceleration of the system by using the total mass and applied force. Then, use Newton's second law for individual objects to find the forces on them.

Answer 1

The Correct Option is C

Let the force applied on A be \( F = 100 \, \text{N} \), and the masses of A and B be \( m_A = 7 \, \text{kg} \) and \( m_B = 3 \, \text{kg} \), respectively.
The total mass of the system is: \[ m_{\text{total}} = m_A + m_B = 7 \, \text{kg} + 3 \, \text{kg} = 10 \, \text{kg} \] Now, the acceleration of the system is given by: \[ a = \frac{F}{m_{\text{total}}} = \frac{100}{10} = 10 \, \text{m/s}^2 \] The force on A, which is exerted on B, can be calculated using Newton's second law for the body B: \[ F_B = m_B \times a = 3 \times 10 = 30 \, \text{N} \] Thus, the force on A applied to B is \( 30 \, \text{N} \).