Coefficient of static friction

A coffee cup on the horizontal dashboard of a car slides forward when the driver decelerates from 44.4 km/hr to rest in 3.65 s or less, but not if he decelerates in a longer time. What is the coefficient of static friction between the cup and the dash? Thank you!

magnitude of string tension

Hi. Can someone show me how to do the the following problem? "A mass M of 2.71 kg is attached to the end of a string whose length is 0.640 m, and is whirled in a vertical circle in the same radius about a fixed point. Find the magnitude of the tension when the mass is at the top if its speed at the top is 5.73 m/s." (I don ...continues

speed around a curve

"A train traveling at a constant speed rounds a curve of radius 286 m. A chandelier suspended from the ceiling swings out to an angle of 15.7 degrees throughout the turn. What is the speed of the train?"

speed of loop-de-loop roller coaster

"At what minimum speed must a roller coaster be traveling when upside down at the top of a circle if the passengers are not to fall out? Assume a radius of curvature of 9.27 m."

acceleration due to gravity above Earth

"How far above the Earth's surface will the acceleration due to gravity be a quarter of what it is on the surface?" I tried to use the g' = (G * m) / r^2 equation (with the mass of the earth as "m") because it was used with a somewhat similar problem in my book about the value of g on the top of Mount Everest, but I came up w ...continues

orbit around moon

"During an Apollo lunar landing mission, the command module continued to orbit around the moon at an altitude of about 100 km. How long did it take to go around the moon once? The radius of the moon is 1738 km."

mass of 2 stars

"Suppose that a binary star system consists of two stars of equal mass. They are observed to be separated by 359 million km and to take 4.50 earth years to orbit about a point midway between them. What is the mass of each?"

simple conversion

"A sprinter accelerates from rest to 10.0 m/s in 1.35 seconds. What is her acceleration in (a) m/s^2, and (b) km/h^2?" I got (a) right. Acceleration = 10/1.35 = 7.41 m/s^2. But I somehow screw it up when I go to do the conversion. Here's what I did: 10 m = 0.01 km 1.35 s = 3.75 x 10^-4 hr (1.35 x (1 hr/3600 s) So the s ...continues

Angular Acceleration

A cylindrical 6.00 kg reel with a radious of .600m and a frictionless axle, starts from rest and speeds up uniformly as a 4.00kg bucket falls into a well. The bucket starts from rest and falls for 4.00s. a) What is the linear acceleration of the falling bucket? b) How far does it drop? c)What is the angular acceleration of t ...continues

constant acceleration

"A speeding motorist traveling 120 km/h passes a stationary police officer. The officer immediately begins pursuit at a constant acceleration of 10.0 km/h/s. How much time will it take for the police officer to reach the speeder, assuming that the speeder maintains a constant speed?" First, I converted 120 km/h into 33 m/s. ...continues