A sports car claims that it can start from rest and reach 60 mph (26.8 m/s) in a

Question

A sports car claims that it can start from rest and reach 60 mph (26.8 m/s) in a distance of 33.5 meters. To reach its maximumm speed, it accelerates at this constant rate for 11.25 seconds.

a) How many seconds does it take to reach 60 mph?
- I got 1.25 seconds
b) What is the maximum speed of this car?
- Using kinematics I got 120.6 m/s
c) If the mass is 1900 kg, what force must the car provide to keep it traveling at this maximum speed ( Hint: don't forget friction) - I know that Fnet= mass x acceleration, and that gives me 1900 x 10.72 = 20,368 N but this is not taking into account friction. What role does friction play and how can I calculate it properly? d) I was driving this car at a maximum speed on a test track when a deer ran out in front of me. My reaction time was 0.5 seconds, before I hit the brakes. Assuming that the engine is no longer applying any forward force, and my wheels lock up, how far will I travel before I come to a stop after seeing the deer (give answer in miles, using: 1 Km = 0.62 miles)? e) How much time will elapse from the time that I see the deer until I stop? A sports car claims that it can start from rest and reach 60 mph (26.8 m/s) in a distance of 33.5 meters. To reach its maximumm speed, it accelerates at this constant rate for 11.25 seconds.

a) How many seconds does it take to reach 60 mph?
- I got 1.25 seconds
b) What is the maximum speed of this car?
- Using kinematics I got 120.6 m/s
c) If the mass is 1900 kg, what force must the car provide to keep it traveling at this maximum speed ( Hint: don't forget friction) - I know that Fnet= mass x acceleration, and that gives me 1900 x 10.72 = 20,368 N but this is not taking into account friction. What role does friction play and how can I calculate it properly? d) I was driving this car at a maximum speed on a test track when a deer ran out in front of me. My reaction time was 0.5 seconds, before I hit the brakes. Assuming that the engine is no longer applying any forward force, and my wheels lock up, how far will I travel before I come to a stop after seeing the deer (give answer in miles, using: 1 Km = 0.62 miles)? e) How much time will elapse from the time that I see the deer until I stop?

Explanation / Answer

(c) Well NET force=mass x acceleration. You have only one force acting on the car in this equation, because the car is moving at a constant speed without any forces acting on it to increase the speed. However, you have the force of friction (Ffriction) acting on the car trying to slow it down. On the FBD Ffriction points left, making it a negative vector, so your equation would be -Ffriction=ma. or -(Fn x mu)=ma. (d) For this one you can use COE. K=Q .5mv^2=mg(mu)d (e) If you have the initial and final velocity plus the distance and the acceleration to stop, you can just use either the second or third kinematic equations

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