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NEET PHYSICSEasy

A horizontal force 10 N10 \text{ N} is applied to a block A as shown in figure. The mass of blocks A and B are 2 kg2 \text{ kg} and 3 kg3 \text{ kg}, respectively. The blocks slide over a frictionless surface. The force exerted by block A on block B is:

A

4 N

B

6 N

C

10 N

D

zero

Step-by-Step Solution

  1. Analyze the System: Since the blocks are in contact and moving on a frictionless surface under a single external force, they move together with a common acceleration (aa).
  2. Calculate Acceleration: Consider blocks A and B as a single system.
  • Total mass M=mA+mB=2 kg+3 kg=5 kgM = m_A + m_B = 2 \text{ kg} + 3 \text{ kg} = 5 \text{ kg}.
  • Net external force F=10 NF = 10 \text{ N}.
  • According to Newton's Second Law: a=FM=105=2 m/s2a = \frac{F}{M} = \frac{10}{5} = 2 \text{ m/s}^2 [Source 32]
  1. Calculate Contact Force: Isolate block B. The only horizontal force acting on it is the contact force exerted by block A (FABF_{AB}).
  • Apply Newton's Second Law to block B: FAB=mB×aF_{AB} = m_B \times a FAB=3 kg×2 m/s2=6 NF_{AB} = 3 \text{ kg} \times 2 \text{ m/s}^2 = 6 \text{ N}
  • Alternatively, considering block A: FFBA=mAa    10FBA=2(2)    FBA=6 NF - F_{BA} = m_A a \implies 10 - F_{BA} = 2(2) \implies F_{BA} = 6 \text{ N}. By Newton's Third Law, the force A exerts on B is equal in magnitude. [Source 110, 115]
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