Biology Forums - Study Force

If a bike skids to a stop we have the displacement(length of skid mark) and final velocity (0m/s). How can I calculate the other variables with just these two pieces of information? A direct formula or explanation would be nice.
How do car accident investigators calculate initial speed and acceleration than?

You need at least 3 pieces of information to solve for one kinematics quantity.

Emm.. the only equation i can think of is

S= UT + 0.5AT^2

where U= initial velocity, T= time period, S is displacement (distance), and A is acceleration.

EDIT: I just realised you didnt have the acceleration.... i don't think theres another way to solve the equation.

You don't have enough information to get all three.

For example, let the initial velocity be v0, arbitrarily.
If so, then v0*t = 2d, and -v0^2 = 2*a*d.  Using algebra, t = 2d/v0 and a = -v0^2/(2d).
Now if we substitute into the final equation, v0 + at = 0, we get v0 - (2d/v0)*(v0^2/(2d)) = v0 - v0 = 0.  This can always be satisified, no matter what the initial velocity is.

Look at it this way.  If the bike was going at 20mph and stopped in 50 ft, then it slowed down at a certain speed.  If the bike was going 60mph (hypothetically) and stopped in 50ft, it just slowed down a lot faster.

Accident investigators make some assumptions based on results of tests. They know some typical things like expected deceleration of a car (usually, some might know about bicycles) with the brakes locked.  You would have to do some testing to add information to the data you have.