Calculate the force on the other support

In summary, a uniform thin rod of weight 100 N is supported horizontally by two bricks at its ends. At t=0 one of these bricks is kicked out quickly. The force on the other support immediately thereafter can be calculated using the equation Mg(L/2)sin(theta), where M is the mass of the rod, g is the acceleration due to gravity, L is the length of the rod, and theta is the angle of the rod with respect to the horizontal. However, since the length is not given, it can be eliminated from the equation using dimensional analysis. The resulting constant in the equation would be determined by working through the standard equations for linear acceleration versus force and angular acceleration versus torque, using unknowns for mass, length
  • #1
H_Ab
2
0

Homework Statement


A uniform thin rod of weight 100 N is supported horizontally by two bricks at its
ends. At t=0 one of these bricks is kicked out quickly. Calculate the force on the
other support immediately thereafter.

Homework Equations


I'm not sure if I am on the right track with this equation since I don't have the length and from what I know, I need the length for torque problems: Mg(L/2)sin(theta)

The Attempt at a Solution


I thought since each brick has a force of 50N that if one brick is locked the force on the supporting brick is -50N since it's a downward force. Please help me with the equation and how to go about it. Thanks
 
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  • #2
H_Ab said:
I'm not sure if I am on the right track with this equation since I don't have the length and from what I know, I need the length for torque problems: Mg(L/2)sin(theta)
Follow that through and see what happens. Maybe the length will not feature in the answer.
(From dimensional analysis, you can predict that it won't. Given an acceleration (g) a mass and a length as input, and a force to be the result of multiplying and dividing these and raising them to powers, the only combination that works is acceleration * mass * constant.)
 
  • #3
So what would my constant be? My weight would be 50N since it's for one brick, and my acceleration is 9.81m/s. I'm confused about the constant.
 
  • #4
H_Ab said:
So what would my constant be?
You need to determine that by working through the usual equations.
Create unknowns for mass, length, angular acceleration and write out the standard equations for linear acceleration versus force and angular acceleration versus torque.
 
  • #5
I would approach this problem by first drawing a free body diagram of the rod and the forces acting on it. The forces acting on the rod are its weight (100 N) acting downwards, and the reaction force from the two supports acting upwards. Since one of the supports is kicked out, the reaction force from that support will no longer be present. This means that the only force acting on the remaining support is the weight of the rod (100 N).

Using Newton's second law, F=ma, we can calculate the acceleration of the rod immediately after the support is kicked out. Since the rod is initially at rest and there is no net force acting on it, the acceleration will be 0 m/s^2.

Next, we can use the equation F=ma again to calculate the reaction force on the remaining support. Since the acceleration is 0 m/s^2, the reaction force must also be 0 N. This means that there is no force acting on the remaining support immediately after the other support is kicked out.

In summary, the force on the other support immediately after the support is kicked out is 0 N. This makes sense intuitively, as the rod is no longer being supported and will start to fall due to its weight.
 

1. What is the equation used to calculate the force on the other support?

The equation used to calculate the force on the other support is F = mg, where F is the force, m is the mass of the object, and g is the acceleration due to gravity.

2. How do you determine the mass of the object in order to calculate the force?

The mass of the object can be determined by using a scale or by knowing the density and volume of the object and using the equation m = ρV, where m is the mass, ρ is the density, and V is the volume.

3. What is the value of acceleration due to gravity used in the calculation?

The value of acceleration due to gravity varies depending on the location and altitude. On Earth, it is typically taken as 9.8 m/s². However, for more precise calculations, the exact value can be determined using the equation g = Gm/r², where G is the universal gravitational constant, m is the mass of the planet, and r is the distance from the center of the planet.

4. Can the force on the other support be negative?

Yes, the force on the other support can be negative if the force is acting in the opposite direction of the support. This can happen if the object is accelerating downwards or if the support is being pulled downwards.

5. Is there a limit to the distance between the object and the support in order for this calculation to be accurate?

The distance between the object and the support does not affect the accuracy of the calculation, as long as the object is not too far away from the support. If the distance is too large, the gravitational force between the object and the support may be affected by other objects, making the calculation less accurate.

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