Homework Help: Physics

Posted by Phil on Thursday, September 16, 2010 at 9:06am.

A 1100 kg car is moving toward the north along a straight road at a speed of 20.0 m/s. The driver applies the brakes and the car comes to rest in a distance of 140 m.

(a) If the road is completely level, what is the constant force applied to the car to bring it to rest? (Remember to specify the direction.)

(b) If the road goes down a hill at a 4 degree angle with respect to the horizontal, what is the constant force applied to the car to bring it to rest?

(c) What is the source of the force that brings the car to rest? (In other words, what is exerting the force on the car?) Explain your answer clearly.
No one has answered this question yet.

Physics - drwls, Thursday, September 16, 2010 at 10:01am
(a) Calculate accleration (a)
V^2 = 2 aX. a = V^2/(2X)
Then use
F = ma
for the force required to stop in that distance. It will be in the backwards direction

(b) Add M g sin(4 degrees) to the previous answer. It is the weight component along the direction of motion. It will oincrease the negative stopping force required.

(c) The road applies the stopping force to the tires, when the brakes are applied and wheels do not turn freely.

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