Question

A ball of mass m is thrown upward and another ball of same mass is thrown downward so as to move freely under gravity. The acceleration of centre of mass is


(1) g


(2)2g


(3) 2g


(4) 0

Answer 1

acm=m1a1+m2a2/m1+m2

so we have the acceleration to be calculated as gravity

put a1=-g. Because it is moving upward

a2= g it is falling down

put it in formula you will get

acm= 0