A rifle of mass M is initially at rest but free to recoil. It fires a bullet of mass m and velocity v (relative to the ground). After firing, the velocity of the rifle (relative to the ground) is:.a. –mv. b. –Mv/m.
c. –mv/M.
d. –v.
e. mv/M.

Option C) -mv / M is the correct answer

Explanation:

given that;

A rifle of mass M is initially at rest but free to recoil

velocity = v

using conversation of moment

pi = pf

i.e initial moment = final moment

But initial moment was zero (0) since everything  was rest but free to recoil

so

pi = pf

0 = mv + MV

V is the recoil velocity of the rifle

MV = -mv

V = -mv / M

Therefore Option C) -mv / M is the correct answer

momentum of soft ball three times less than baskey ball

your answer is, orbit around the nucleus