a motorist travelling with a constant speed of 15 m/s passes a school zone sign where the speed limit is 10 m/s. Just as the motorist passes, a police officer on a motorcycle starts off at the same school zone sign in pursuit with constant acceleration of 20 m/s^2.

Question

anonymous · Answer

Well I assume you are asking when he catches the motorist
Lets start off by taking the board sign as the origin
Now lets say they meet after  time t
Dist.travelled by motorist in time t=10t
By policeman=$$20(t^2)$$
Now equate them because that is where they meet
You get two answers t=0 and t=2

anonymous · Answer

ah no thats wrong

anonymous · Answer

Go on explain why

anonymous · Answer

t=0.75s
v=v0+at

anonymous · Answer

What?

anonymous · Answer

velocity = initial velocity + acceleration*time

anonymous · Answer

So what the motorist didn't have any acceleration.And I equated the distance travelled by both now the velocities

anonymous · Answer

his is constant

anonymous · Answer

Yeah so what's you point

anonymous · Answer

lol oops forgot to post this part LOL
(a)How much time elapses before the officer catches up with the motorcycle?
(b)What is the total distance that each have travelled at that point?

anonymous · Answer

Well he catches after 2 seconds at a distance 20 m later

anonymous · Answer

just checking answer...i forgot to post a bit of the question
(a)How much time elapses before the officer catches up with the motorcycle?
(b)What is the total distance that each have travelled at that point?

anonymous · Answer

5.65m?

anonymous · Answer

sorry 5.625

anonymous · Answer

and 0.75s

anonymous · Answer

after t seconds the motorist goes 15t meters, i believe the formula for distance is d=v_ot+1/2at^2

anonymous · Answer

But the policeman's initial velocity was 0

anonymous · Answer

Oh I forgot and kept initial velocity for biker as 10 instead of 15

anonymous · Answer

Anyway just change the numbers

anonymous · Answer

yes, so 15t=1/2*20t^2

anonymous · Answer

Yeah that'd give you the answer

anonymous · Answer

but t=.75s? and so answer is 5.625?

anonymous · Answer

t=1.5s

anonymous · Answer

total distance travelled is 15(1.5)=22.5m

anonymous · Answer

ohhh so you use a quadratic to find t in d=v_ot+1/2at^2

anonymous · Answer

i was using v=vo+at

anonymous · Answer

so if there is distance involved you have to use that formula...

anonymous · Answer

first you have to equate 15t with v_ot+1/2at^2, solve for t, then solve for d

anonymous · Answer

distance traveled by motorist in t seconds is 15t, distance travelled by cop in t seconds is
10t^2,

anonymous · Answer

haha thanks