Question

Two heavy bodies of mass m and 3m tied
together with a light string of mass
density u are dropped from a helicopt as
shown . A constant air friction forca f
acts on both of them is the length of
the string is l determine the time taken
by a pulse to go from top to batton of
the string​

Answer 1

Thus the time taken  by a pulse to go from top to bottom of  the string​ is t = l √ 2μ / F

Explanation:

Mass of bodies = m and 3 m

As we know that:

• 3 mg - ( T + F) = 3 mg ----(i)
• T + mg - F = ma ------(ii)

3 mg - T - F = 3 T + 3 mg - 3 F

2 F = 4 T

T = F  / 2

V = √ T / μ  = √ F / 2 μ

t = l/ v

t = l √ 2μ / F

Thus the time taken  by a pulse to go from top to bottom of  the string​ is

t = l √ 2μ / F