# physics

A driver sees a horse on the road and applies the brakes so hard that they lock and the car skids to stop in 24 m .The road is level ,and the coefficient of kinetic friction between tires and the road is 0.7.How fast was the car going when the brakes were applied?

1. 👍
2. 👎
3. 👁
1. weight = m g
so F = -mu m g =- 0.7 * m * 9.81 =- 6.87 m
so acceleration = - 6.87 m/s^2
v = Vi + a t
0 = Vi - 6.87 t
t = Vi/6.87
average speed = Vi/2
so
24 = (Vi/2)(Vi/6.87)
Vi^2 = 329.8
Vi = 18.2 m/s

1. 👍
2. 👎
2. M*g = 9.8M = Wt. of vehicle = Normal(Fn).

Fp = Mg*sin A = 9.8M*sin 0 = 0. = Force parallel with surface.

Fk = u*Fn = 0.7 * 9.8M = 6.86M N. = Force of kinetic friction.

Fp - Fk = M*a,
0 - 6.86M = M*a,
a = -6.86 m/s^2.

V^2 = Vo^2 + 2a*d = 0,
Vo^2 - 13.72*24 = 0,
Vo = 18.1 m/s.

1. 👍
2. 👎

## Similar Questions

1. ### Physics

A driver of a car going 90.0km/h suddenly sees the lights of a barrier 40.0 metres ahead. It takes the driver 0.75 seconds before she applies the brakes, and the average acceleration during braking is -10.0 m/s squared. Does the

2. ### Physics

A car accelerates in the +x direction from rest with a constant acceleration of a1 = 1.76 m/s2 for t1 = 20 s. At that point the driver notices a tree limb that has fallen on the road and brakes hard for t2 = 5 s with a constant

3. ### Physics

A car is traveling at 11.0 m/s, and the driver sees a traffic light turn red. After .59 s (the reaction time), the driver applies the brakes, and the car decelerates at 8 m/s^2. What is the stopping distance of the car, as

4. ### Physics

The speed limit in a school zone is 40km/h. A driver traveling at this speed sees a child run into the road 13m ahead of his car. He applies the breaks, and the car decelerates at uniform rate of 0.8m/s². If the driver's reaction

1. ### Physics

A car traveling at 20m/s when the driver sees a child standing in the road. He takes 0.80s to react, then steps on the brakes and slows at 7.0m/s^2. How far does the car go before it stops?

2. ### physics

A car is traveling 20 m/s when the driver sees a child standing on the road. He takes 0.8 s to react, then steps on the brakes and slows at 7.0 m/s2. How far does the car go before it stops?

3. ### physics

a car is traveling 20.0 m/s when the driver sees a child standing in the road. he takes 0.80 seconds to react, then steps on the brakes and slows at -7.0 m/s squared. how far does the car go before it stops?

4. ### physics

Two cars are traveling along a straight line in the same direction, the lead car at 26 m/s and the other car at 40 m/s. At the moment the cars are 49 m apart, the lead driver applies the brakes, causing the car to have a

1. ### college physics

a woman driving at a speed of 23 m/s sees a deer on the road ahead and applies the brakes when she is 210m from the deer. if the deer does not move and the car stops right before it hits the deer, what is the acceleration provided

2. ### physics

A car has a mass of 1500 kg. If the driver applies the brakes while on a gravel road, the maximum friction force that the tires can provide without skidding is about 7000 N. If the car is moving at 18 m/s, what is the shortest

3. ### Physics

A 1000-kg car is driving 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 a rest in a distance of 140 m. What is the constant force applied to the car to bring it to

4. ### physics

The driver of a car, traveling at a constant 25 m/s, sees a child suddenly run into the road. It takes the driver 0.45s to hit the brakes. As it slows, the car has a steady acceleration of 8.5 m/s^2. What's the total distance the