# 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 the centre of mass is

Piyush Kumar Behera
417 Points
7 years ago
The acceleration of the centre of mass is the net force on the centre of mass,as only gravitational force due to the earth is acting on both the bodies so the net force on the centre of mass of the bodies will be only gravitational force .So the acceleration of the centre of mass is g(=9.8m/s2).Alternatively you can also calculate using the formula of acceleration of centre of mass=m1a1+m2a2/m1+m2.You will get the same answer.IF you still couldnt get it you can ask again.
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sharan
11 Points
6 years ago
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
Piyush Kumar Behera
417 Points
6 years ago
@sharan,Please dont forget that the acceleration of both the bodies that is m1 and m2 both are downwards.You are taking opposite signs of both of them.Please verify your answer because if you take downward direction as negative.Then the answer of yours must be
acm=m1a1+m2a2/m1+m2
So we have the acceleration to be calculated as gravity
put a1= – g.  Because it is moving upward but the acceleration is downward
a2= – g it is falling down
Put it in formula you will get
acm= – g