Help! I Need Assistance with a Physics Problem

In summary: The velocity vector at t= 0 would be -18\sin(51.43(0))i+ 18 cos(51.43(0))j= 0i+ 18j= 18j. The acceleration vector would be -18(51.43)\cos(51.43(0))i- 18(51.43)\sin(51.43(0))j= -18(51.43)j. The acceleration vector at t= 0 is -18(51.43)j. At t= 0.1 seconds, the position vector is 0.35 cos(51.43(0.1))i+ 0.35
  • #1
brad sue
281
0
Hi I really need help for this problem:

A mass is tethered to a post and moves in a circular path of radius r=.35m
on an air table -friction free- at a constant speed v=18m/s.
We employ the coordinate system ( classic 2 dimension space).
If at t=0s the mass is at θ=0o,
a-what is the coordinates(x,y) of the mass at t=0.1s?
b-what is thye acceleration vector at t=0s?
c-what is the acceleration vector of the mass when θ=90o?

Can someone help meI have noo idea!

the testbook give those answer
a-(0.15m,-0.32m)
b-(-9.3*102m/s2)i
c-(-9.3*102m/s2)j


But first, i need to understand what is going on in the problem.

Thank you for your help
 
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  • #2
Circular motion problem

Hi Brad sue,

the first thing that you want to do for a problem of this type is to establish a proper coordinate system based on the problem and the contraints established. In your case, the problem is one of circular motion, and you are restricted to using Cartesian coordinates (incidentally, using polar coordinates is much more useful for problems involving any kind of circular path).

So, you should set up your Cartesian system, then show the path that the object traces out. Here, you should begin to see something.

Next, take all the information that is given to you in the problem, and try to make sense of it all. For example, the problem indicates what the radius of the circle is (which is useful, say, to find the circumference of the circle). Next, you are given the velocity of the mass (which is useful, say, to figure out how long it takes to go around the circumference of the circle). Moreover, you will also be able to find the angular velocity of the mass. Using this basic information and a little trigonometry, you should be able to solve the problem without a hitch; if not, post what you have done and we'll see where you got stuck.

--
joelperr
 
  • #3
A circle of radius 0.35 m has circumference [itex]0.7\pi[/itex] m. At 18 m/s, the puck will complete a full circle ([itex]2\pi[/itex]radians) in [itex]\frac{0.7\pi}{18}[/itex] seconds and so has an angular velocity of [itex]\frac{2\pi}{\frac{0.7\pi}{18}}= \frac{36}{0.7}[/itex] radians per second. That's about 51.43 radians per second.

What I would do (since this is in the college homework forum) is write the position vector as 0.35 cos(51.43t)i+ 0.35 sin(51.43t)j. The derivative of that is the velocity vector and the second derivative is the acceleration vector.
 

1. What is the best approach to solving a physics problem?

The best approach to solving a physics problem is to first identify the given information, organize it in a clear and logical manner, and then apply the appropriate equations and principles to solve for the unknown variable.

2. How do I know which equation to use for a specific problem?

The equation to use for a specific problem depends on the given information and the unknown variable. It is important to carefully read the problem and identify the relevant variables before selecting an equation to use.

3. Can I use more than one equation to solve a problem?

Yes, it is often necessary to use more than one equation to solve a physics problem. This is especially true for more complex problems that involve multiple variables and principles.

4. What should I do if I am stuck on a problem?

If you are stuck on a problem, take a step back and review the given information and your approach. Sometimes, looking at a problem from a different perspective or breaking it down into smaller parts can help. You can also seek assistance from a teacher, tutor, or classmate.

5. How can I check my answer to make sure it is correct?

To check your answer, you can plug it back into the original equation and see if it satisfies all the given information. You can also use estimation and common sense to ensure that your answer is reasonable.

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