Question

Why does a block of plastic released under water come up to the surface of water?

Answer 1

Hi frnd,
The density of plastic is less than that of water, so the force of buoyancy on plastic will be greater than the weight of plastic displaced. Hence, the acceleration of plastic block will he in upward direction, and comes up to the surface of water.
hope it helped

Answer 2

$<font color= "geen">$ This \:is \: because $<font color= "dark red">$upthrust \: or \:buoyant \: force $<font color= "geen">$acting\: on\: the\: block $<font color= "geen">$of\: plastic\: is\: greater\: than\: the $<font color= "dark red">$gravitational\: force $<font color= "Geen">$acting on the block in the downward direction.