question_answer

  In an experiment, a small steel ball falls through a liquid at a constant speed of 10 cm/s. If the steel ball is pulled upward with a force equal to twice its effective weight, how fast will it move upward?            [JEE ONLINE 25-04-2013]

A)  5 cm/s 

B)  Zero

C)  10 cm/s

D)                   20 cm/s

Correct Answer: C

Solution :

[c]

Weight of the body

and

When the body attains terminal velocity net force acting on the body is zero. i.e., W-T-F=0

And terminal velocity

As in case of upward motion upward force is twice its effective weight, therefore, it will move with same speed 10 cm/s