Theory question 107
DynamicsA light inextensible string passes over a smooth pulley and carries masses 4 kg and 3 kg at its ends. If the masses are released from rest, calculate: (a) their acceleration; (b) their speed after 3 seconds. [Take g = 10 ms−2]
Show the model answer
Model answer
(a) 4 kg: 40 − T = 4a; 3 kg: T − 30 = 3a. Adding: 10 = 7a, a = 10/7 ≈ 1.43 ms⁻².
(b) v = u + at = 0 + (10/7)(3) = 30/7 ≈ 4.29 ms⁻¹.
Explanation
Write F = ma for each mass separately and add to remove the tension.