Question about Centripetal Force

In summary: That is not very realistic.In summary, the conversation is about solving question 2.b. from a physics paper, which involves rearranging equations and finding the angle theta. The original poster initially got 52 degrees as their answer, while the mark scheme says it is 36 degrees. They then discuss how to use the given information to solve for theta and the correct value for mass. The conversation ends with a remark on the questionable accuracy and practicality of the problem.
  • #1
27
1

Homework Statement


Question 2.b. from this paper - http://www.sqa.org.uk/files_ccc/PhysicsEQPAH.pdf

Homework Equations


let theta = x
Tcosx = mg
Tsinx = 2.5 (2.5 is the centripetal force)

The Attempt at a Solution


I rearranged the above equations and got 52 degrees as my answer. The mark scheme(at the bottom of the same document says it's 36 degrees.
 
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  • #2
Maybe you can write down your way to find the angle?
You use the information you gave to get ##\tan \theta?##
 
  • #3
tommyxu3 said:
Maybe you can write down your way to find the angle?
You use the information you gave to get ##\tan \theta?##
I did that and I got 52 degrees as my answer. The mark scheme says 36 but I'm not too sure if they used the correct value for mass.
 
  • #4
Banker said:
I did that and I got 52 degrees as my answer. The mark scheme says 36 but I'm not too sure if they used the correct value for mass.

You will need to show your working for people to help you properly. You haven't said at all how you use the angular velocity, for example.
 
  • #5
PeroK said:
You will need to show your working for people to help you properly. You haven't said at all how you use the angular velocity, for example.
F = mrw^2
F = 0.2(0.35)(6)^2
Central force = 2.5 N
Let Tension = T and the angle theta = x
From the diagram, Tcosx = mg
Tsinx = central force
hence Tsinx = 2.5
Dividing the first eq by the second:
Tsinx/Tcosx = 2.5/mg
Simplifying gives tanx = 2.5/mg
Weight, mg, = 0.2 x 9.8 (0.2kg is the mass of the plane)
hence tanx = 1.28
x = 52 degrees.
 
  • #6
Banker said:
F = mrw^2
F = 0.2(0.35)(6)^2
Central force = 2.5 N
Let Tension = T and the angle theta = x
From the diagram, Tcosx = mg
Tsinx = central force
hence Tsinx = 2.5
Dividing the first eq by the second:
Tsinx/Tcosx = 2.5/mg
Simplifying gives tanx = 2.5/mg
Weight, mg, = 0.2 x 9.8 (0.2kg is the mass of the plane)
hence tanx = 1.28
x = 52 degrees.

You're correct. You can see in the solution that they put ##0.35## for the mass. The funny thing is that the answer is independent of the mass of the plane! There was never any need to use the mass. I guess even the people who set these questions don't like algebra!
 
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  • #7
PeroK said:
You're correct. You can see in the solution that they put ##0.35## for the mass. The funny thing is that the answer is independent of the mass of the plane! There was never any need to use the mass. I guess even the people who set these questions don't like algebra!
Ahh thank you for the clarification! Yeah the Scottish qualifications board are subpar compared their English counterparts.
 
  • #8
Banker said:
Ahh thank you for the clarification! Yeah the Scottish qualifications board are subpar compared their English counterparts.
I can't believe that!
 
  • #9
I also got 52 degrees as my answer.
 
  • #10
PeroK said:
You're correct. You can see in the solution that they put ##0.35## for the mass. The funny thing is that the answer is independent of the mass of the plane! There was never any need to use the mass. I guess even the people who set these questions don't like algebra!
It's worse than that. For part b they used the centripetal force calculated in part a. In part a, the correct mass was used, but in part b they got confused between the mass number, 0.2, and the radius number, 0.35. So in their calculation the masses did not cancel, which is why they got the wrong answer for the angle.
It's also a bit naughty that you have to pretend the plane develops no lift.
 

1. What is centripetal force?

Centripetal force is the force that acts towards the center of a circular path, keeping an object moving in a circular motion.

2. How is centripetal force different from centrifugal force?

Centripetal force is the force that keeps an object moving in a circular path, while centrifugal force is the apparent outward force experienced by an object in circular motion.

3. What is the formula for calculating centripetal force?

The formula for calculating centripetal force is Fc = (mv^2)/r, where Fc is the centripetal force, m is the mass of the object, v is the velocity, and r is the radius of the circular path.

4. What are some real-life examples of centripetal force?

Some examples of centripetal force include the motion of planets around the sun, the rotation of a car around a curved road, and the swinging of a pendulum.

5. How does centripetal force relate to Newton's laws of motion?

Centripetal force is related to Newton's first law of motion, which states that an object in motion will continue in a straight line at a constant speed unless acted upon by an external force. In the case of circular motion, the external force is the centripetal force that keeps the object moving in a circular path.

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