question_answer

Three blocks of masses m, 3m and 5m are connected by massless strings and pulled by a force F on a frictionless surface as shown in the figure below. The tension P in the first string is 16 N If the point of application of F is changed as given below The value of P and Q shall be

A)  16 N, 10 N                          

B)  10 N, 16 N

C)  8 N, 2 N                              

D)  10 N, 6 N

Correct Answer: C

Solution :

                 Case I                                                                 P = 16N                 Tension \[Q=\left( \frac{3m+m}{m+3m+5m} \right)\times F\]                                 \[16=\frac{8}{9}\]                                 F = 18 N                 Case II                                 Tension \[Q=\left( \frac{3m+m}{m+3m+5m} \right)\times F\]                                                 \[=\frac{4}{9}\times 18\]                                                 = 8 N                   Tension \[P=\left( \frac{m}{m+3m+5m} \right)\times F\]                                                 \[=\frac{18}{9}\]                                                 = 2 N