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)

90 N

Answer 2

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) $\left( 10 + \frac{5}{4} \right) = 90 \, N$