PHYSICS · Multi-part · CBSE · Physics · System of Particles and Rotational Motion · System of Particles and Rotational Motion
Problem
Blocks P and Q, of masses 2.5kg and 4.0kg, are connected by a light spring that is initially neither stretched nor compressed. The blocks rest on a horizontal, frictionless surface. A constant horizontal force F0 is applied to Block P toward the right. The spring remains attached and massless.
A debate arises between two students:
• Student 1 claims that the acceleration of each block is a=F0/(mP+mQ) because the spring force is internal.
• Student 2 argues that the spring force must be included when applying Newton’s second law to each block, so the acceleration cannot be found that way.
Respond to the prompts below, using clear, concise reasoning. No numerical values of F0 are required in your answers.
(a) For the instant just after F0 is applied, identify all forces acting on Block P and all forces acting on Block Q.
(b) Explain whether the spring force alters the acceleration of the center of mass of the two-block system.
(c) Decide which student’s argument is correct. Provide a qualitative justification that explicitly references Newton’s laws and the distinction between internal and external forces.