A disc of mass 15g is held suspended in air by throwing
20
marbles per second vertically upwards. Mass of each marble is
5
g
. Then the velocity with which the marbles are thrown is:
[ Assume that the marbles rebound with the same speed after striking the disc ]
(a)
0.55
m
/
s
(b)
0.65
m
/
s
(c)
0.75
m
/
s
(d)
0.85
m
/
s
