# physics

A car (mass = 750 kg) is initially moving with velocity 30 m/s. The driver slowly presses on the brakes and bring the car to a stop, traveling 50 m in the process. Calculate the force of friction between the car and the ground that brings it to a stop. Draw a free-body diagram for the car and clearly explain the method behind your solution.

1. 3
asked by Cassie
1. F * d = work done by friction = initial Ke = (1/2) m v^2

F * 50 = (1/2)(750)(900)
100 F = 750 * 900
F = 750 * 9

There are harder ways of course using
F = change of momentum/ time = 750*30/t
then
50 = (1/2)a t^2
where a = 30/t
so
100 = 30 t
t = 10/3 seconds to stop
a = 9 m/s^2 (about 1 g)
F = m a = 750* 9

posted by Damon

## Similar Questions

1. ### College Physics

Most of us know intuitively that in a head-on collision between a large dump truck and a subcompact car, you are better off being in the truck than in the car. Why is this? Many people imagine that the collision force exerted on
2. ### Physics (Help Please)

Most of us know intuitively that in a head-on collision between a large dump truck and a subcompact car, you are better off being in the truck than in the car. Why is this? Many people imagine that the collision force exerted on
3. ### physics ( please help me)

a railroad handcar is moving along striaght, fricionless tracks. In each of the following cases the car initially has a total mass (car and contents of magniude 4.00 m/s^1. Find the final velocity of the car in each of the three
4. ### Physics

A drunken driver crashes his car into a parked car that has its brakes set. The two cars move off together (perfectly inelastic collision), with the locked wheels of the parked car leaving skid marks 6.0 m in length. If the mass
5. ### Physics

Most of us know intuitively that in a head-on collision between a large dump truck and a subcompact car, you are better off being in the truck than in the car. Why is this? Many people imagine that the collision force exerted on
6. ### Physics

A car with mass of 1875kg is traveling along a country road when the driver sees a deer dart out onto the road. The driver slams on the brakes manages to stop before hitting the deer. The driver of a second car with 2135kg is
7. ### Physics

A railroad car with a mass of 12400 kg collides and couples with a second car of mass 18700 kg that is initially at rest. The first car is moving with a speed of 7.7 m/s prior to the collision. (a) What is the initial momentum of
8. ### Physics &gt;.&lt;

A big truck has a mass of 5,000kg. It is moving down the road at a velocity of 15m/s. As it approaches a stop sign, the driver tries to stop, but the truck slides on ice and hits a car (mass = 500kg) that is stopped. After the
9. ### physics

A compact car, mass 755 kg, is moving at 1.00 ✕ 102 km/h toward the east. The driver of the compact car suddenly applies the brakes hard for 1.8 s. As a result, an average force of 5.8 ✕ 103 N is exerted on the car to slow it
10. ### Science

A driver of a moving car at 20m/s finds a child on the road 50m ahead and stops the car 10m earlier to the child. If the mass of the car with driver is 1000kg, calculate the force exerted by the brakes of the car??

More Similar Questions