Deceleration to stopping point, with snapshot times/speeds

mathematical physicsphysicsprojectile motion

Simple question but I've confused myself over-complicating it.

  • Say initial speed is 72ms
  • distance is 0 (increasing)
  • deceleration rate fixed at -2.2mss

How far and what time will it take to stop?

The tricky part then is I need to calculate the snapshot time and speed when it hits various milestone distances (area under Vt-graph) such as 900m, 600m, 300m, TO GO until the end of the stopping distance.

ie, total stopping distance of 1200m, then:

  • at 900m from the end stopping point (zero speed) what is the current time/speed.
  • at 300m from the end stopping point, what is the current time/speed.

EDIT

In the diagram, after covering 500metres (A+B) what is the current speed and time at this point.

enter image description here

Many thanks

Best Answer

$A)$ use $v_f=v_i +at$ to find when the final velocity equals zero.

$B)$ When you have the time, use $0=(v_i)^2 +2ad$ to solve for the distance, d the car will travel before stopping.

Then when you have total distance, subtract the distance you want such as $900$ to plug in equation $(v_f)^2=(v_i)^2 +2ad$.

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