Circular motion-what is the radius of the loop de loop in meters

Click For Summary

Homework Help Overview

The problem involves a scenario where Snoopy is flying a vintage warplane in a circular path, specifically a "loop de loop." The context includes his speed at the bottom of the loop and the reading on bathroom scales indicating he weighs four times his normal weight. The objective is to determine the radius of the loop.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss converting speed from km/hr to m/s and the implications of the weight reading on the scales. There are attempts to apply centripetal acceleration and force equations, with some expressing confusion about the relevance of certain forces and how to approach the problem.

Discussion Status

The discussion is ongoing with various participants exploring different aspects of the problem. Some have suggested focusing on the forces acting on Snoopy, while others are questioning the assumptions made regarding mass and acceleration. There is no explicit consensus, but several participants are providing guidance on identifying relevant equations and forces.

Contextual Notes

Participants are grappling with the implications of the weight reading and how it relates to the forces acting on Snoopy during circular motion. There is a noted lack of clarity regarding the mass of Snoopy and how it factors into the calculations, as well as confusion about the necessary equations to use.

  • #31
vela said:
There are only two forces on Snoopy: the gravitational force and normal force. The net force on Snoopy results in his centripetal acceleration.

Yes that is correct.
But I am looking at the force that had put the body in circular motion.
What can supply this force?
As OP has stated in one of his equations, Fc.
What are the sources that supply Fc

Surely one of the candidates is the spring of the scale.
 
Physics news on Phys.org
  • #32
if I got an answer R=255m... does this seem plausible?
 
  • #33
Show us your calculations.
 
  • #34
v=180km/h=50m/s

ac=v2/R
(9.8m/s2)=(50m/s)2/R

solved for R=255.10m... Probably wrong
 
  • #35
Close, but the value you used for ac isn't correct. You need to find the acceleration using F=ma. Find the net force F on Snoopy and divide by his mass to find a. That will be the value of a you need in your calculation.
 
  • #36
but I don't have his mass... or is his mass 4*g=4*(9.8m/s^2)?
 
  • #37
[Snoopy] is sitting on a set of bathroom scales that him he weighs four times what he normally.
Say he has mass m. It'll turn out to cancel out in the end, as is often the case, so we don't actually need to know its value.

All these F=ma problems start with identifying what forces act on the body. You have to get this part right, otherwise the rest won't work out. That's why it's almost always a good idea to draw a free-body diagram with the forces. In this problem, there are two forces acting on Snoopy, his weight and the normal force. So start by answering these questions.

In terms of m and g, what is his weight w? In what direction does the force of gravity pull on him?

In terms of m and g, what is the magnitude of the force N exerted on him by the scale? In what direction does this force act on him?

Now add the two forces together, remembering they are vectors so that they're directions matter. What is the net force on Snoopy?
 
  • #38
You keep saying in terms on m and g, but I thought m canceled out? Sorry its hard for me to picture it without seeing it in front of me
 
  • #39
It cancels out in the end when you solve for the acceleration, but it's present in the expressions for weight and the normal force.

What I want you to do is write down the equation that will let you solve for the acceleration, and you will see that when you solve for it, the mass drops out in the end. It's often the case you won't know what a particular quantity, like Snoopy's mass, is equal to, but you just give it a name and use it in the equations and see where it leads.
 
  • #40
is the a=g/4?
 
  • #41
No. Answer these questions and post your answers here:
In terms of m and g, what is his weight w? In what direction does the force of gravity pull on him?

In terms of m and g, what is the magnitude of the force N exerted on him by the scale? In what direction does this force act on him?

Now add the two forces together, remembering they are vectors so that they're directions matter. What is the net force on Snoopy?
 
  • #42
There's Fg pulling downwards and 4FN pushing up?
 
  • #43
his weight would be Fg=m*g=9.8m/s2 pulling downwards?

FN=4*m*a? pulling upwards?
 
  • #44
the m is messing me up and i don't know why
 
  • #45
dani123 said:
There's Fg pulling downwards and 4FN pushing up?
Those are the correct directions. The 4FN isn't quite right. See below.
dani123 said:
his weight would be Fg=m*g=9.8m/s2 pulling downwards?
Good. Fg=mg. You can't get rid of the m just yet.
FN=4*m*a? pulling upwards?
No, this isn't right. The problem says the scale reads four times what he normally weighs. He normally weighs Fg, which we know is equal to mg, so FN is four times that, that is, FN=4mg.

Now sum the two forces. What's the net force on Snoopy?
 
  • #46
net force on Snoopy would be 5mg?
 
  • #47
No, you have to remember forces are vectors. FN points upward while Fg points downward, so they partially cancel.
 
  • #48
Oh ops! I knew that... so its 3mg right?
 
  • #49
Right! So you have Fnet=3mg, and Newton's 2nd law tells you that equals ma.
 
  • #50
So now I solve for a=3g=29.4m/s2

and then plug that into my acceleration equation from earlier and solve for the radius which should give me R=85m ... Does this seem reasonable?
 
  • #51
Yup! That's right!
 
  • #52
thank you so much for your help and patience! along with everyone else who helped, it is greatly appreciated!
 

Similar threads

Loop problem with skier on ramp going into a loop-the-loop
  • · Replies 13 ·
Replies
13
Views
2K
Circular loop of wire is concentric with a solenoid
  • · Replies 10 ·
Replies
10
Views
5K
Circular motion - ball in a loop
  • · Replies 19 ·
Replies
19
Views
4K
Circular motion: normal force on a loop
  • · Replies 7 ·
Replies
7
Views
3K
Circular motion , the loop the loop
  • · Replies 3 ·
Replies
3
Views
3K
Magnetic field in a circular loop
  • · Replies 6 ·
Replies
6
Views
8K
Teardrop loop-de-loop radius function
  • · Replies 1 ·
Replies
1
Views
2K
Electromotive force (EMF) of a circular loop wire
  • · Replies 3 ·
Replies
3
Views
2K
Circular loop with uniform magnetic field
  • · Replies 5 ·
Replies
5
Views
4K
Displacement Function of an Idealized Circular Loop Coaster
  • · Replies 21 ·
Replies
21
Views
2K