imagine you are standing on the bank of a river observing a fish drifting in the

Question

imagine you are standing on the bank of a river observing a fish drifting in the river's current. You stand stationary and notice the following. Initially the fish is not swimming , it drifts with the current at speed vc. At time t0=0, the fish begins to swim, accelerating upstream with a constant acceleration a=.6ft/s2.

A) according to your observation, after accelerating for t=5s the fish is moving upstream with velocity v=2.0ft/s. what is the speed of the river's current, vc?

B) Find the fish's water speed after it has been accelerating for t2=7s. according to you, what would the fish's speed be at this moment?

C) at what time t according to you does the fish have speed v=0.

Explanation / Answer

A)
Initial velocity = vc
acceleration = -0.6 ft/s^2
after 5 sec,
the velocity = vc-0.6*5 = vc-3 = -2
vc = 1 ft/sec
B) at t = 7 sec, the velocity w.r.t water = 4.2 ft/sec upstream
speed with respect to observer = 1-4.2 ft/sec = 3.2 ft/s upstream.
C) velocity according to me = 0 when vc-a*t = 0
or 1 = 0.6*t
t = 1/0.6 sec
t = 1.67 sec.

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