(a) Calculate the force (in N) needed to bring a 900 kg car...

(a) Calculate the force (in N) needed to bring a 900 kg car to rest from a speed of 95.0 km/h in a distance of 105 m (a fairly typical distance for a non-panic stop). N (b) Suppose instead the car hits a concrete abutment at full speed and is brought to a stop in 2.00 m. Calculate the force exerted on the car and compare it with the force found in part (a). force in (b) / force in (a) =

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00:01 Okay, we want to calculate the force that's required to bring this 900 kilogram car to rest, given its initial speed, and its stopping distance.

00:12 Okay, so if we want to calculate the force on the car, let's just think about what that force is going to be.

00:25 So here's our car, it's got a normal force upward, gravitational force down, and it's slowing down, right? so it's going to have this force to the left.

00:38 That's slowing it down.

00:39 That's the force required to stop it.

00:42 So if we apply newton's second law, some of the forces in the x direction we'll do is ma.

00:49 So negative f equals ma, so f equals minus ma.

01:02 So we need to find the acceleration of this car, and then that will tell us the force required.

01:07 Well, we can calculate the acceleration.

01:10 Using kinematics.

01:12 So v final squared equals v initial squared plus two times the acceleration times the distance it takes to stop.

01:22 It stops so the final velocity is zero.

01:26 The initial velocity is given in kilometers per hour.

01:31 We need to convert that to meters per second.

01:35 It's around 26 .4 meters per second.

01:42 So the acceleration is negative of the initial velocity squared over two...

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