posted by Rachel on .
A professor drives off with his car (mass 840 kg), but forgot to take his coffee mug (mass 0.37 kg) off the roof. The coefficient of static friction between the mug and the roof is 0.7, and the coefficient of kinetic friction is 0.4. What is the maximum acceleration of the car, so the mug does not slide off?
maximum friction force = .7 *.37*9.8
2.53 = m a
a = 2.53/.37 = 6.86 or .7 g of course
As we all know, once it starts sliding, that is the ball game.
Moreover the mass of the vehicle is also a red herring.