# My method was correct right?, sorry to post again I just wanted to double check that I had the setup right:

A 8000N car is traveling 12 m/s along a horizntal road when the brakes are applied. The car skids to a stop in 4.0s. How much kinetic energy does the car have.

my work:

W= 8000N/9.18m/s

mass= 815.49 kg

Kinetic energy= (1/2mv^2-1/2mv^2)

kinetic energy=1/2 (815.49)(0)^2 - 1/2 (815.49)(12 m/s)^2 =5.0 X 10^4 J

One more question:

A sled weighs 3000N. It is pulled on level ground by a dog team. The coefficient for kinetic friction is 0.03. How much work is done by the dog team in pulling the sled 500m at a constant speed?

My work:

Friction coefficient is F=coefficient *N= (.03 * 3000N)= 90N

W= F*d= 90N * 500m=45000J

is the solving method good

Method is correct. I don't agree with your calculation of 5.0E4. I assume the value for g was a typo.

yes on the sled work.

## Yes, your method for both questions is correct. However, there was a mistake in your calculation for the kinetic energy of the car.

Let's go through each question step by step:

1. For the car's kinetic energy:

- The weight of the car is given as 8000N.

- The velocity of the car is given as 12 m/s.

- The car skids to a stop in 4.0s.

To find the kinetic energy, we can use the formula: Kinetic energy = 1/2 * mass * velocity^2.

First, let's calculate the mass of the car:

- Weight = mass * gravity, where gravity is approximately 9.8 m/s^2.

- So, mass = weight / gravity = 8000N / 9.8 m/s^2 ≈ 816 kg.

Now we can calculate the kinetic energy:

- Kinetic energy = 1/2 * mass * velocity^2

- Substituting the values: Kinetic energy = 1/2 * 816 kg * (12 m/s)^2 = 5.88 × 10^4 J (to two significant figures).

So, the correct answer for the kinetic energy of the car is approximately 5.88 × 10^4 J.

2. For the sled's work:

- The weight of the sled is given as 3000N.

- The coefficient of kinetic friction is given as 0.03.

- The sled is pulled for a distance of 500m at a constant speed.

To find the work done, we can use the formula: Work = Force * distance.

First, let's calculate the force of friction:

- Force of friction = coefficient of friction * normal force.

- The normal force is equal to the weight of the sled, which is 3000N.

- So, force of friction = 0.03 * 3000N = 90N.

Now we can calculate the work done:

- Work = Force * distance

- Substituting the values: Work = 90N * 500m = 45000 J.

So, the correct answer for the work done by the dog team in pulling the sled is 45000 J.

In summary, your method for both questions is correct, but there were slight errors in the calculations for the kinetic energy of the car.