A forgetful adjunct Loyola physics instructor while leaving the restaurant where

Question

A forgetful adjunct Loyola physics instructor while leaving the restaurant where he has been dining out, leaves his wallet and iPhone on top of his 2004 Mazda3 hatchback. He pulls out of the restaurant parking lot, turns onto Veterans Blvd, and accelerates to approximately 25 miles per hour before stopping with traffic at a red light, upon which the iPhone and wallet slide down the car windscreen and land on the wipers, startling the driver.

a) is static or kinetic friction primarily responsible here for preserving his valuables? Justify your answer. Extra credit if you draw a free-body diagram

b) Calculate the amount of frictional force necessary to keep the iPhone in place during the acceleration and constant motion at 25 mph (Hint: convert to metric first!)

Explanation / Answer

a) as initially , while accelerating and moving the car ,

phone and wallet reamins at rest during the motion wrt the car

there is static friction acting on the valuables for most time

and it is primarily responsible here for preserving his valuables

b)

speed , v = 25 mph = 11.2 m/s

acceleration of his car , a = 3.37 m/s^2 ( internet source )

Now , friction force needed on iphone = mass * acceleration

friction force needed on iphone = 0.129 * 3.37

friction force needed on iphone = 0.44 N

the friction force needed on iphone is 0.44 N

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