Question

Suppose you take a thin, weightless plastic baggie, and fill it with seawater that weighs 100 N. You seal the baggie, being sure there are no air bubbles. Now you tie the baggie to the end of a rope, and lower it into the ocean.  F, the magnitude of the force you must exert on the rope to support the weight of the baggie, is

Multiple Choice:

A.		zero
B.		more than 100 N
C.		cannot tell- need more information
D.		100 N
E.		more than zero, less than 100 N

Answer 1

In the air when we hold the baggie with Rope tension in the rope will be same as downward force that is its weight hence Tension in the rope in that case will be 200N

But when,

When we lower the baggie into ocean some bouyant force will act in the baggie with sea water. And this bouyant force will be equal to weight of water displaced.

As the sea water in bag displace same volume of water as of itself hence weight of water displaced will same as weight of water in bad , as both water are of same density.

Hence downward weight and upward bouyant force will cancel out each other. Thus tension in Rope will be zero.

HENCE OPTION 1 WILL BE CORRECT.