Physics HW help? Normal Force between two objects?

In summary, A horizontal force is applied to block 1, and the acceleration of all three blocks is found to be 3.4 m/s2. M2 is the mass of block 2, and is 11.29 kg. The normal force between blocks 2 and 3 is 40.8 N.
  • #1
VoNi
3
0
Physics HW help!? Normal Force between two objects?

Hi, I've had trouble trying to gigure out this problem! I would really appreciate the help!

The Problem:

Three blocks rest on a frictionless, horizontal table (see figure below), with m1 = 7 kg and m3 = 12 kg. A horizontal force F = 103 N is applied to block 1, and the acceleration of all three blocks is found to be 3.4 m/s2.

A. Find m2
B. What is the normal force between blocks 2 and 3?
I coouldnt post the figure(picture) but I can explain it.. The three blocks are all lined up against each other. So block 1(m1) is first, then block two(m2) is right next to block1, then block 3(m3) is against block 2.. they are all lined up on top of the table.. side by side..
Relevant equation:

I found the mass of block 2 by doing F=ma. or M= F/A
7+12+m2= 103/3.4
19+m2= 30.29
m2= 11.29

So M2 is 11.29

My only problem is that I don't know how to find the normal force between blocks 2 and 3


Attempt at a Solution:

The way i tried to find the solution was figuring out what force is acting on block three so that it can accelerate 3.4 m/s^2.
I did:
F=m*a
F=12*3.4
F= 40.8

Now, is 40.8 the normal force between block two and three or is that just an irrelevant number?

Thank you so much for the help!
 
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  • #2


VoNi said:
The way i tried to find the solution was figuring out what force is acting on block three so that it can accelerate 3.4 m/s^2.
very good.
I did:
F=m*a
F=12*3.4
F= 40.8
Yes, but don't forget, F is actually F_net (in Newtons, don't forget the units)
Now, is 40.8 the normal force between block two and three or is that just an irrelevant number?
It is very relevant. If F_net = 40.8 N, what forces act on that block in the x direction? Draw a free body diagram of block 3. Is F_net and and F_normal the same??
 
  • #3


Thank you SO much! that was very helpful! and the normal force, is 40.8 N. Thanks for taking the time to help me out! =)
 
  • #4


You are welcome. Note that the normal force should probably (I think) be rounded off to 41 N (it's a significant figure thing), but your answer is essentially correct. Wecome to PF!
 

1. What is the normal force between two objects?

The normal force is the support force exerted by a surface on an object that is in contact with it. It is always perpendicular to the surface and prevents the object from falling through the surface.

2. How is the normal force calculated?

The normal force is calculated by multiplying the mass of the object by the acceleration due to gravity, and then multiplying that by the cosine of the angle between the surface and the force of gravity.

3. What factors affect the normal force?

The normal force is affected by the mass of the object, the angle of the surface, and the force of gravity. It is also affected by any external forces acting on the object, such as friction or tension.

4. Can the normal force be greater than the weight of an object?

Yes, the normal force can be greater than the weight of an object. This occurs when the object is accelerating or when it is on an inclined plane, as the normal force must be strong enough to counteract the force of gravity and prevent the object from moving.

5. How does the normal force change in different situations?

The normal force can change in different situations depending on the variables mentioned above. For example, if the mass or angle of the surface changes, the normal force will also change. Additionally, if external forces are applied to the object, the normal force may need to increase to maintain equilibrium.

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