Moving at 20m/s a carr of mass 2000kg applies its brakes and comes to rest over a distance of 10m. Find the size of the net force that acted to stop the car.

would I find t using t=dv. then would I use that for F=(m*v)/t ?

The speed doesn't stay constant, so that won't work. The simplest way to solve the problem is to use that the work done by the force must equal the kinetic energy. So:

F*d = 1/2 m v^2

To find the net force that acted to stop the car, you can use the work-energy principle. The work done by the net force is equal to the change in kinetic energy.

The work done by the force (F) is given by the equation:

Work (W) = Force (F) * distance (d)

According to the problem, the car comes to rest over a distance of 10m, so the work done by the force is:

W = F * 10

The change in kinetic energy can be calculated using the equation:

Change in kinetic energy (ΔKE) = final kinetic energy (KE_final) - initial kinetic energy (KE_initial)

The initial kinetic energy of the car is given by:

KE_initial = 1/2 * mass (m) * initial velocity squared (v_initial^2)

The final kinetic energy is zero since the car comes to rest:

KE_final = 1/2 * mass (m) * final velocity squared (v_final^2) = 0

Therefore, the change in kinetic energy is:

ΔKE = KE_final - KE_initial = -1/2 * m * v_initial^2

According to the work-energy principle, the work done by the net force is equal to the change in kinetic energy, so we have:

W = ΔKE

F * 10 = -1/2 * m * v_initial^2

Now, plug in the given values into the equation:

F * 10 = -1/2 * 2000kg * (20m/s)^2

Simplifying the equation:

F * 10 = -1/2 * 2000kg * 400m^2/s^2

F * 10 = -400000 N·m

Dividing both sides by 10:

F = -40000 N

So, the size of the net force that acted to stop the car is 40000 N. Note that the negative sign indicates that the force acted in the opposite direction of motion.