Help Solving Motorcycle Braking Problem | Reaction Time, Acceleration, Distance

[ConnorPhys]

A motorcyclist sees an obstacle and comes to a complete stop. Given are reaction time (0.8seconds), acceleration once started braking (-6.5meters/seconds^2), and total distance traveled (35meters) from initial sighting to complete stop. Solve to find initial velocity and time from when he started braking to when he stopped.

I can't figure out a single formula to use that will help me find one of the unknowns and solve the problem! Please help!

 

[haruspex]

You must know some equations relating to uniform acceleration. (The acronym SUVAT is often used.)

 

[NascentOxygen]

A motorcyclist sees an obstacle and comes to a complete stop. Given are reaction time (0.8seconds), acceleration once started braking (-6.5meters/seconds^2), and total distance traveled (35meters) from initial sighting to complete stop. Solve to find initial velocity and time from when he started braking to when he stopped.

I can't figure out a single formula to use that will help me find one of the unknowns and solve the problem! Please help!

Neither can I ! Certainly not until I have first condensed the wordy problem sentences into a familiar mathematical form, e.g.,

v_f = 0 m/sec
reaction time t = 0.8 secs
total distance d = 35m
...

v_i = ?? m/sec

That done, the next step is to write down all the equations of motion that you know. Then go through them one by one, ticking off the variables you know or need, until you have highlighted by multiple ticks some likely candidates to use for solving this.

 

[willem2]

Suppose you did know the speed of the motor cyclist. call it v. Could you compute the distance traveled during the reaction time, and the distance traveled when breaking?
Set the stopping distance equal to the sum of those two distances and solve for v.