A particle of mass m falls from rest through a resistive medium having resistive force, F = -kv, where v is the velocity of the particle and k is a constant. Which of the following graphs represents velocity (v) versus time (t) ?
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Answer
(4) [figure]
Solution
m dvdt = mg - kv
0v dvmg - kv = 0t dtm
- 1k mg - kvmg = tm
v = mgk (1 - e-kt/m )
At t = 0, v = 0; v increases with a decreasing slope ( dvdt = g e-kt/m) and approaches the terminal velocity mgk.
This is graph (4).
Answer: (4)