Assume that the small-massed particle is 
and the heavier mass particle is 
.
Now, by momentum conservation and energy conservation:
Now, there are 2 solutions but, one of them is useless to this question's main point so I excluded that point. Ask me in the comments if you want the excluded solution too.
So now, we see that 
and 
. So therefore, the smaller mass recoils out.
Hope this helps you!
Bye!
Answer:
C.) 1.5 kg
Explanation:
Start with the equation:
Plug in what you know, and solve:
Find matching soluation:
C.) 1.5 kg
The pertinent equation here is F=ma. You haven't shared the mass of the box, so I will use M to represent that mass.
Then F = M(<span>2.3 m/s^2) (answer)</span>
