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Car curves at a radius of 50m while travelling at 100km/hr

  • Thread starter MissJewels
  • Start date
  • #1
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Homework Statement



Calculate the centripetal acceleration module in the following cases as a multiple of g = 9.8 m / s ^ 2.
a) a car traveling at 100km / h on a curve of radius 50m.
b) a jet plane flying at 1,500 km / h and making a turning radius of 5km.
c) a stone that is rotated every 0.5 s after a string of length 1 m
d) a speck of dust on the edge of a disk of 30 cm diameter rotating at 33.33333 ... rev / min.
e) a molecule in a centrifugal radius of 15cm rotating at 30,000 rev / min.


Homework Equations


a)

g= 9.8 m/s2
ar = v2/r
ar = ug

u: coefficient of friction(WHERE DO I GET THIS?!)

haven't touched b) and on yet..

The Attempt at a Solution


so heres how i began...
converted:
vi = 100km/h = 10 000m/3600s = 27,78m/s
ar= 1002/50 = 200 m/s2

ar = 9,8u

Okay... so how do i get the coefficient of friction(u) if im not given any mass value?
 

Answers and Replies

  • #2
374
1
You don't need the coefficient of Friction for these problems. Convert the velocity to m/s. Square it and divide by the radius in meters to get ac. Divide by 9.8 to get the multiple.

You will need to find the angular velocity for some of these problems and be able to convert from revolutions/min to radians/sec
 
  • #3
34
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You don't need the coefficient of Friction for these problems. Convert the velocity to m/s. Square it and divide by the radius in meters to get ac. Divide by 9.8 to get the multiple.

You will need to find the angular velocity for some of these problems and be able to convert from revolutions/min to radians/sec
That's awesome, thanks! I got a, b, and c, but im stuck on d ... given its diameter, where do i go from there?
 
Last edited:
  • #4
374
1
Remember that ac=r*ω2 you have r you need to find ω, the angular velocity. The units are radians/sec. The stone makes 1 revolution in .5 seconds. 1 revolution is how many radians? Divide that number by 0.5 sec
 
  • #5
34
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Remember that ac=r*ω2 you have r you need to find ω, the angular velocity. The units are radians/sec. The stone makes 1 revolution in .5 seconds. 1 revolution is how many radians? Divide that number by 0.5 sec
I got it, thanks!
 
  • #6
34
0
You don't need the coefficient of Friction for these problems. Convert the velocity to m/s. Square it and divide by the radius in meters to get ac. Divide by 9.8 to get the multiple.

You will need to find the angular velocity for some of these problems and be able to convert from revolutions/min to radians/sec
I'm doing the d right now...
found that r= 0,015m
w = 0,349 rad/s
and used the equation:
ac=r*ω2
and got ac= 0,0018

then divided it by 9,8.... and got 1,84 x10^-4g........ when the right answer should just be 1,87g
HELP?
 
Last edited:
  • #7
374
1
radius is not .015m
ω is not .349 rad/s
Recheck these values and recalculate
 

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