Two blocks with masses m and M are pushed along a horizontal frictionless surface by a horizontal applied force as shown.The magnitude of the force of either of these blocks on the other is:
A)mF/(m +
B)mF/M
C)mF/(M - m)
D)MF/(M + m)
E)MF/m

Question

Two blocks with masses m and M are pushed along a horizontal frictionless surface by a horizontal applied force  as shown.The magnitude of the force of either of these blocks on the other is: 
A)mF/(m + 
B)mF/M 
C)mF/(M - m) 
D)MF/(M + m) 
E)MF/m

Quizplus · Accepted Answer

According to Newton's third law of motion, the force of block with mass m on block with mass M is equal and opposite to the force of block with mass M on block with mass m. Therefore, we only need to consider the force of block with mass m on block with mass M. 
The acceleration of both blocks is the same, as they are being pushed together. We can find the acceleration using the formula: 
F_applied = (m+M)a  
where F_applied is the applied force. 
Rearranging this formula gives: 
a = F_applied/(m+M) 
Now, using Newton's second law of motion, the force of block with mass m on M is: 
F = ma = m(F_applied/(m+M))  
Simplifying this equation gives: 
F = mF_applied/(m+M) 
Therefore, the magnitude of the force of block with mass m on block with mass M is mF_applied/(m+M). Hence the answer is A.

Two Blocks with Masses M and M Are Pushed Along