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# AS mechanics Questions? Please explain how to answer this question? watch

1. A car's velocity increases from 5ms to 25ms on a 100m straight stretch or road. The acceleration is constant.

Find the speed of the car when it has travelled 50m.

2. (Original post by BuuTuu)
A car's velocity increases from 5ms to 25ms on a 100m straight stretch or road. The acceleration is constant.

Find the speed of the car when it has travelled 50m.

Just as a nitpick it should be m/s or ms^-1, it's fairly important.

But on to the question, "constant acceleration" should mean SUVAT equations to you.

s=
u=
v=
a=
t=

Put in what you know and what you want to find out and recall the correct equation that uses the information you have. (You'll want to find the acceleration first. You can do that by considering the whole motion from 0 to 100m)
3. Okay, use suvat (displacement, initial velocity, final velocity, acceleration, time).

So:
s = 100
u = 5
v = 25
a = ?
t = ?

So you need to work out acceleration, so you do v^2 = u^2 + 2as and get 25^2 = 5^2 + (2)(a)(100) and then get 625 = 25 + 200a and then rearrange to get a = 600/200 = 3m/s^2

So now you have your CONSTANT acceleration and you need to use suvat again to show the speed when the car has traveled half the distance:
s = 50
u = 5
v = ?
a = 3
t = ?

Use v^2 = u^2 + 2as again to get v^2 = 25 + 300 = 325, so v = 325^(1/2) ~ 18.03...

Hope this makes sense!
4. Alrite. what you have is initial velocity of 5m/s and a final velocity of 25m/s. The distance travelled is 100 m. so u can find the acceleration using the formula
v^2 = u^2 + 2as (v= 25, u= 5, s = 100)
This would give you the acceleration which would be 3.
Now you can see that the question says acceleration is constant so use the same formula i.e. v^2 = u^2 + 2as but this time to find v i.e. final velocity when distance travelled is 50m.
Therefore, v = ?, u = 5 (same), a = 3 (que says const.) n s = 50.
This would give you 18.03 as your final velocity after travelling 50m. I hope it helped.\m/
5. s= (v+u)t / 2 Find total time

a = (v-u) / t Find constant acceleration

v^2 = u^2 + 2as Find velocity
6. Thanks everyone

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Updated: September 28, 2011
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