Physics Help-Car Crash Opposing Forces
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Physics Help-Car Crash Opposing Forces

[From: ] [author: ] [Date: 11-08-27] [Hit: ]
assuming that the force was constant.Let’s use average force to determine the average acceleration!Average force = mass * average acceleration½ * 5 * 10^6 * 0.0188 = 3000 * average accelerationaverage acceleration = 15.67 m/s^2The average force caused the velocity to decrease to 0 m/s as the car moved 0.0188 meter.......

KE = ½ * 5 * 10^6 * 0.0188^2
½ * 3000 * v^2 = ½ * 5 * 10^6 * 0.0188^2
Solve for v

3000 * v^2 = 5 * 10^6 * 0.0188^2
v = 0.768 m/s

You solved for acceleration, assuming that the force was constant.
Let’s use average force to determine the average acceleration!
Average force = mass * average acceleration
½ * 5 * 10^6 * 0.0188 = 3000 * average acceleration
average acceleration = 15.67 m/s^2

The average force caused the velocity to decrease to 0 m/s as the car moved 0.0188 meter.
So the acceleration is negative. (-15.67 m/s^2)
The following equation is useful, when you have acceleration and distance, but do not know the elapsed time.
vf^2 - vi^2 + (2 * a *d)
vf = 0
d = 0.0188
a = -15.67
0 – vi^2 = 2 * -15.67 * 0.0188
vi =(2 * -15.67 * 0.0188)^0.5 = 0.767 m/s^2

You can get the correct answer if you use the average acceleration!!

Force * time = mass * change of velocity
Not F * distance = mass * change of velocity

I hope this helps you!!

-
This is an energy problem.
PE = KE
½kx² = ½mv²

v = x*√(k/m) = .0188*√(5E6/3000) = .7675 m/s
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