PHYSICS 1403, QUIZ 3, Chapter 5, October 14, 2004
Partial credit will be LIBERAL, provided that you show your work!
USE BACK IF NECESSARY! (Please tell me that you have done so!)
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1. (12 points). The maximum speed with which a car mass of mass m = 2500 kg can round a
curve on a flat road is v = 20 m/s. The figure is a top view. The curve’s radius is r = 75 m.
There is (static) friction between the road and the tires, or the car wouldn’t stay on the curve.
a. If the car is going at this maximum speed, compute the centripetal acceleration it
experiences. Compute the centripetal force it experiences. What phenomenon causes
this force?
2.
b.
Compute the maximum static friction force between the tires and the road. (Hint: You don’t
need to know the coefficient of friction to answer this!)
c.
Compute the coefficient of static friction between the tires and the road.
(18 points). See figure. A planet, mass m = 1.3 x 1025 kg, is in a circular orbit at constant speed
around a star. The orbit radius (measured from the star’s center) is r = 2.2 x 1011 m. The mass of
the star is M = 3.1 x 1030 kg. G = 6.67 x 10-11 N m2/kg2.
a. Compute the gravitational force of attraction between the planet and the star.
circular orbit!
b.
Compute the centripetal force and the centripetal acceleration experienced by the planet. What
is their direction? (Hint: You don’t need to know the planet’s speed to answer this! Use the
results of part a along with Newton’s 2nd Law!).
c.
Use the results of part b to compute the planet’s speed in orbit. Note: Einstein’s Special
Theory of Relativity tells us that NOTHING can move faster than the speed of light, which is
c = 3 x 108 m/s! If you get a speed greater than this (or even a significant fraction of it!)
SOMETHING IS WRONG with your calculation!
d.
Compute the period of this planet’s orbit. Note: Your answer should be something
reasonable for a planet’s period! If you get a period of only a few seconds (or less!) or one of
billions of years, SOMETHING IS WRONG with your calculation!