A small iron ball falls through a viscous liquid at a constant speed of 20cm/sec. If the steel ball is pulled upwards with a force equal to twice its effective weight, how will it move upward?
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a
with constantly increasing speed
b
with constantly decreasing speed
c
with the same speed
d
will be at rest without any movement
answer is C.
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Detailed Solution
For the first case, B+6πηrv=mgFor the second case, F+B=mg+6πηrvt2mg−2B+B=mg+6πηrvt⇒mg−B=6πηrvtSolving we get, v= 20 cm/sec