- #1
musicfairy
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There's two force problems I couldn't get on my study guide.
1. Two blocks (A and B) are in contact on a horizontal frictionless surface. A 36-N constant force is applied to A as shown. The magnitude of the force of A on B is:
There is a picture. Block B is on the right of Block A. 36N is applied to block A. Block A = 4.0kg and block B = 20kg.
A. 1.5 N
B. 6.0 N
C. 29 N
D. 30 N
E. 36 N
What I did is:
F = (mA + mB)a
a = 36 / (4.0 + 20)
a = 3/2 m/s2
FAB = 4.0(3/2)
= 6.0 N
The correct answer is D. 30N. I can see where it comes from. I thought "the magnitude of the force of A on B" means I should multiply mA and a to get the force, but to get 30 N they multiplied mB and a. Why?
2. Two blocks with masses m and M are pushed along a horizontal frictionless surface by a horizontal applied force F as shown. The magnitude of the force of either of these blocks on the other is:
In this picture. M and m are in contact. m is on the right of M. Force F is applied to M.
A. mF/(m + M)
B. mF/M
C. mF/(M - m)
D. MF/(m + M)
E. MF/m
The correct answer is A. I don't even know how to start this problem. I tried to solve for a and substitute but that failed. Any ideas?
These came from a study guide I was given in class. I thought I knew this topic well but these problems really scare me. Can someone please explain these to me? I have a test coming up pretty soon. I read this section in the book, but sometimes I can't apply what I read to every problem.
1. Two blocks (A and B) are in contact on a horizontal frictionless surface. A 36-N constant force is applied to A as shown. The magnitude of the force of A on B is:
There is a picture. Block B is on the right of Block A. 36N is applied to block A. Block A = 4.0kg and block B = 20kg.
A. 1.5 N
B. 6.0 N
C. 29 N
D. 30 N
E. 36 N
What I did is:
F = (mA + mB)a
a = 36 / (4.0 + 20)
a = 3/2 m/s2
FAB = 4.0(3/2)
= 6.0 N
The correct answer is D. 30N. I can see where it comes from. I thought "the magnitude of the force of A on B" means I should multiply mA and a to get the force, but to get 30 N they multiplied mB and a. Why?
2. Two blocks with masses m and M are pushed along a horizontal frictionless surface by a horizontal applied force F as shown. The magnitude of the force of either of these blocks on the other is:
In this picture. M and m are in contact. m is on the right of M. Force F is applied to M.
A. mF/(m + M)
B. mF/M
C. mF/(M - m)
D. MF/(m + M)
E. MF/m
The correct answer is A. I don't even know how to start this problem. I tried to solve for a and substitute but that failed. Any ideas?
These came from a study guide I was given in class. I thought I knew this topic well but these problems really scare me. Can someone please explain these to me? I have a test coming up pretty soon. I read this section in the book, but sometimes I can't apply what I read to every problem.