# Homework Help: Three questions. Uniform circ. motion, non-uniform circ. motion, and weightlessness.

1. Sep 21, 2009

### tjohn101

1. The problem statement, all variables and given/known data

1) Estimate the force a person must exert on a string attached to a 0.100 kg ball to make the ball revolve in a circle when the length of the string is 0.600 m. The ball makes 1.00 revolutions per second. Do not ignore the weight of the ball. In particular, find the magnitude of FT, and the angle ϕ it makes with the horizontal. [Hint: Set the horizontal component of FT equal to maR; also, since there is no vertical motion, what can you say about the vertical component of FT?]

FT= N
ϕ= °

2) A car at the Indianapolis-500 accelerates uniformly from the pit area, going from rest to 285 km/h in a semicircular arc with a radius of 194 m.

Determine the tangential acceleration of the car when it is halfway through the turn, assuming constant tangential acceleration.
m/s2

Determine the radial acceleration of the car at this time.
m/s2

If the curve were flat, what would the coefficient of static friction have to be between the tires and the roadbed to provide this acceleration with no slipping or skidding?

3) DONE

2. Relevant equations
1) unsure.
2) unsure.
3) DONE

3. The attempt at a solution

1) for FT, used FT=m*(v^2/r), but was unsure of what to use for r. It also says to not ignore the weight, but what do I do with it?

2) I don't even know where to start.

3) DONE

I've been trying at these three for almost 3 days now. I have looked through the book and researched, but with no luck. Any help is greatly appreciated. Thank you!

Last edited: Sep 21, 2009
2. Sep 22, 2009

### Redbelly98

Staff Emeritus
Re: Three questions. Uniform circ. motion, non-uniform circ. motion, and weightlessne

Reread the hint. The horizontal component of FT is mv2/r. FT itself is not a horizontal force, but acts at some angle.