Question

Two 5kg masses are attached to opposite ends of a long mass less cord which passes tautly over a mass less friction less pulley. The upper mass is initially held at rest on a table 50 cm from the pulley. The coefficient of kinetic friction between this mass and the table is 0.2. When the system is released, its resulting acceleration is closest to which of the following? 

(A) 9.8 m/s² 

(B) 7.8 m/s² 

 (C) 4.9 m/s² 

(D) 3.9 m/s² 

(E) 1.9 m/s²  

Answer 1

Correct option (D) 3.9 m/s²

ΣF_external = m_totala gives (5kg × 9.8m/s²) – F_f = (10kg)a, where F_f is the force of friction acting on the 5kg block on the table: µmg = 0.2 × 5kg × 9.8m/s² = 9.8N