# Math Help - displacement

1. ## displacement

A car is moving along a straight road. It passes a point A. After t second its distance, s m, from A is given by s = 10t - tsquared

a) find the time when the car passes through A again?

Don't know

b) find ds/dt? = 10 - 2t

c) find the maximum distance of the car from A.

We need to find ds/dt = 0
10 - 2t = 0
10 = 2t
t = 5 seconds

d) find the speed of the car 3 seconds after the passing of A.
10 - 6 = 4m/s

e) find the acceleration of the car

f''(x) which is -2

Please could someone help with question a) and check the rest? Many thanks in advance.

2. b - d are fine.

For a), it's asking you "when does the car get back to A?", in other words, "when is the distance from A again 0?".

So it's asking you to find t when s = 0.

3. Originally Posted by Prove It
b - d are fine.

For a), it's asking you "when does the car get back to A?", in other words, "when is the distance from A again 0?".

So it's asking you to find t when s = 0.

When the acceleration is negative does that mean the car is slowing down?

4. so lets see

10t - tsquared = 0
- tsquared + 10 t = 0

What do you do from here?

5. No, the negative tells the direction it is going in.

For the other part

$-t^2 + 10t = 0$

$t(-t + 10) = 0$

$t = 0$ or $-t + 10 = 0$.

Go from here.

6. or t = 10

Thanks!