physics hw help me again plz ^^ nice ppl?

Question

the highest speed ever achieved on a bucycle was reached by john howard of the U.S ,the bicycle,which was accelerated at 245km/h.Suppose he wants to slow down .and he applies the brakes on his now freely moving bicycle.if the averade acceleration of the bicycle during brakinf is -3.0m/s^2, how long will it take for the bycicle's velocity to decrease by 20%?

Answer 1

3.40 sec

Answer 2

First convert the km/h speed to m/s.
1 km=1000 m
1 hour=60 min=60*60 s=3600 s

Find 20% of that speed. (Multiply by 0.20).

Acceleration is how fast we gain or lose speed. For instance, if I have an acceleration of 5 m/s/s and start at zero speed, then
0 s->0 m/s
1 s->5 m/s
2 s->10 m/s
3 s->15 m/s
4 s->20 m/s

On the other hand, if I have a speed of 20 m/s and I'm losing speed at 5 m/s/s, (a=-5 m/s/s) then I have
0 s->20 m/s
1 s->15 m/s
2 s->10 m/s
3 s->5 m/s
4 s->0 m/s

So it for that example, it takes 4 s to lose all that speed.

I bet you can do the rest from there.