- #1

baztack

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The question reads:

Roberta drives her 1452kg car along a straight, level road at a constant velocity of 30.0 m/s {E}. Her brakes suddenly give out. She puts the car in heutral and lets it coast for 25.0s. The air drag decelerates the car to a velocity of 25.0m/s[E].(Assume a frictionless surface)

A) Draw a freebody diafra, of the car before the breaks give out and while coasting..... I think I got this one right...

B)Determine the avergae accleration furing this interval...

My answer: G: deltaTime - 25.0s, deltaVelocity - 30.0m/s

R: acceleration

A: a=deltav/deltat

s: a = 30/25 =1.2m/s

P: avg acceleration is 1.2m/s

C) Determine the average force of air against the car.

G: Mcar=1452kg, accel=1.2m/s

R: Fair

A: Fair=(m)(accel)

S: Fair=1452kg x 1.2m/s

=1742.4N

P: Avg force of air against the car is 174x10 N.

Im assuming up to this point that my calculations are correct... if you see a problem please hint and let me know...

This is where im running into trouble...

D) After coasting for 25.0s, Roberta pulls her handbrake to slow the car to a stop. If it takes 3.0s to stop the car, what is the force applied by the handbrake? Assume that the force exerted by the air remains constand and is equal to the force determined in part c.

I have my givens mapped out G: m=1452kg, V1=30.0m/s, V2=25.0m/s, T1=25.0s, T2=28.0s, Fair=1742.4N

R: Fapp?

For the rest of the question I was trying to firgure out exactly how to go about finding a solution to this problem. I know that F=m(accel) so should I use an acceleration equation to find the accleration then plug it into the F=M(accel) to get the force of the applied handbrake?

Sorry ive just been stuck on this question now for hours and any help would be greatly appreciated.