Physics - Dynamics of Circular Motion

[dummy123]

I have this problem. I can't do it. I have no idea how to proceed with this.
The question:

"A machine part consists of a thin 40.0 cm-long bar with small 1.15-kg masses fastened by screws to its ends. The screws can support a maximum force of 75.0 N without pulling out. This bar rotates about an axis perpendicular to it at its center.
a) As the bar is turning at a constant rate on a horizontal frictionless surface, what is the maximum speed the masses can have without pulling out the screws?
b) Suppose the machine is redesigned so that the bar turns at a constant rate in a vertical circle. Will one of the screws be more likely to pull out when the mass is at the top of the circle or at the bottom?
c) Using the result of part b), what is the greatest speed the masses can have without pulling a screw?"

I just know that the answer to b) is the bottom.

 

[Deleted member 4993]

I have this problem. I can't do it. I have no idea how to proceed with this.
The question:

"A machine part consists of a thin 40.0 cm-long bar with small 1.15-kg masses fastened by screws to its ends. The screws can support a maximum force of 75.0 N without pulling out. This bar rotates about an axis perpendicular to it at its center.
a) As the bar is turning at a constant rate on a horizontal frictionless surface, what is the maximum speed the masses can have without pulling out the screws?
b) Suppose the machine is redesigned so that the bar turns at a constant rate in a vertical circle. Will one of the screws be more likely to pull out when the mass is at the top of the circle or at the bottom?
c) Using the result of part b), what is the greatest speed the masses can have without pulling a screw?"

I just know that the answer to b) is the bottom.

If I were to do this problem, I would first draw a "dynamic FBD" along with centripetal acceleration of individual parts.

Please show us what you have tried and exactly where you are stuck.

Please follow the rules of posting in this forum, as enunciated at:

READ BEFORE POSTING​

Please share your work/thoughts about this problem.

 

[skeeter]

while rotating in a vertical circle, [MATH]F_c=F_{net}[/MATH] on the lower mass is the vector sum of [MATH]F_s[/MATH], the force the rod exerts on the screws, and [MATH]mg[/MATH], the weight of the mass.

Note that [MATH]F_c = mr \omega^2[/MATH] and [MATH]F_s \le 75 \, N[/MATH]

 

[dummy123]

If I were to do this problem, I would first draw a "dynamic FBD" along with centripetal acceleration of individual parts.

Please show us what you have tried and exactly where you are stuck.

Please follow the rules of posting in this forum, as enunciated at:

READ BEFORE POSTING​

Please share your work/thoughts about this problem.

Well, I don't know what to do with this problem. I have no real work.
I have my variables:
40 cm = radius
1.15 kg = mass
and 75 N = F max

I have this equation:
a= v^2 / R
where R is the radius.
but I don't have acceleration.

therefore F = ma = m * (v^2 / R)
But I don't have v. I'm looking for v max.

I don't know how a diagram can help me here. I drew one and have attached it.

 

[skeeter]

horizontal rotation ...

[math]F_c \le F_{s \, max}[/math]
[math]\dfrac{mv^2}{r} \le 75 \, N[/math]
vertical rotation ...

[math]F_c = \dfrac{mv^2}{r} = F_s - mg \implies F_s = \dfrac{mv^2}{r} + mg \le 75 \, N[/math]