A rubber ball of mass 10 g & volume 15 cc is dipped in water to a depth of 10 m.The time taken to reach the surface is
a. 1 seconds
b. 1.5 seconds
c. 2 seconds
d. 3 seconds
Explain.

Question

A rubber ball of mass 10 g & volume 15 cc is dipped in water to a depth of 10 m.The time taken to reach the surface is
a. 1 seconds
b. 1.5 seconds
c. 2 seconds
d. 3 seconds
Explain.

anonymous · Answer

Buoyant force = weight of displaced water. Since density of water is 1g/cc.
 Buoyant force = 15cc times density of water times g = 15cc * 1g/cc *g 
So, Buoyant force = 15g
 Weight of the ball = 10g 
Net force acting on the ball = buoyant force - weight = 15g - 10g = 5g 
Let the acceleration of the ball is a then force acing on the ball = 10a
 So 10a = 5g
 a = 0.5g
 distance = 1/2at^2 
So 10m = 1/2 0.5*10* t^2 m, taking g = 10m/s^2
 t = 2 sec
 Ans: c