Question
Two bodies of masses 10 kg and 20 kg respectively kept on a smooth, horizontal surface are tied to the ends of a light string. A horizontal force F = 600 N is applied to
(i) A, (ii) B along the direction of string.
What is the tension in the string in each case?
Solution
Horizontal force, F = 600 N
Mass of body A, m1 = 10 kgMass of body B, m2 = 20 kg
Total mass of the system, m = m1 + m2 = 30 kg
Using Newton’s second law of motion,
F = ma
Acceleration (a) produced in the system can be calculated as,
= 
When force is applied on a body A.
Equation of motion can be written as,
F - T = m1a
Therefore,
T = F - m1a
= 600 - 10 x 20
= 400 N ... (i)
When Force is applied on a body B, we have
F - T = m2a
i.e., T = F - m2a
Therefore,
T = 600 - 20 x 20 = 200 N ... (ii)
From (i) and (ii), we can say that the answer is different in both the cases.
Therefore, the answer depends on which end of mass, the force is applied.
