Two blocks of mass 2.9 kg and 1.9 kg are suspended from a rigid support S by two inextensible wires each of length 1 meter, see fig. The upper wire has negligible mass and the lower wire has a uniform mass of `0.2kg//m`. The whole system of blocks wires and support have an upward acceleration of `0.2m//s^2`. Acceleration due to gravity is `9.8m//s^2`.

(i) Find the tension at the mid-point of the lower wire.
(ii) Find the tension at the mid-point of the upper wire.

Answer

(i) 20 (ii) 50

Explanation

(i) Tension at A = ?
Distribution of mass below and above A :
Below `A = 1.9 kg + (0.2 xx 0.5) kg = 2.0 kg`
Above `A = 2.9 kg + (0.2 xx 0.5) kg = 3. kg`
Net tension at `A = (0.9 + 0.1) (g + a) = 2 xx 10 - 20 N`
(ii) Tension at B = ?
All mass is below B. Therefore tension
`= (2.9 + 1.9 + 0.2 xx 1) xx (9.8 + 0.2) = 50.0 N`