Question

A 1400 kg car is traveling at 24 m/s when the driver takes his foot off of the gas. The car eventually rolls to a stop after 225 m. What the force of friction acting on the car?

Answer 1

`1792N`

Explanation:

By Newton's second law, `F = ma`

In this case, the only force is friction.

So `F = 1400 * a`

Lets pause for a moment to find `a`.

Let's use one of the projectile motion equations. We choose this one because it has all the variable we know except for `a` so we can solve for `a`.

`V_f^2 = V_i^2 + 2ad`
`0 = 576 + 2*a*225`
`a = -1.28` (indicating the negative direction)

So back to our original equation:

`F = 1400 * a`
`F = 1400 * -1.28`
`F = 1400 * -1.28`
`=1792N` Opposite the direction of the movement of the car