Question

Two blocks of masses 8 kg and 5 kg are connected with a rod of mass 3 kg (see figure). The upper block is pulled up with a force of 180 N. The tension in the rod in contact with the upper block is

• A. 22.5 N
• B. 45 N
• C. 90 N
• D. 180 N

Answer 1

Answer: (C)

Let the acceleration of the system be a
Then (8 + 3 + 5) a = 180 - 16 $\times$ 10 = 20
That is, $a=\frac{20}{16}=\frac{5}{4}m/s$
Tension at P = (3 + 5) $\times$ (g + a) = (3 + 5) $\left(10+\frac{5}{4}\right)=90N$