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starber · Nov 1, 2011, 08:53 PM

1. A car starts from rest and accelerates at 9.50 m/s^2 for 800. M in the eastward direction.
a) How fast is the car going after this? (I got 7.60 x 10^-6 m, but I think I did it way wrong.)
b) How long did it take to travel 800. m? (So what I did was I used the formula t = change in velocity / a. But my answer was 800 seconds. Oh geez. )

If anyone could give the steps, it'd be great help too!

ebaines · Nov 2, 2011, 05:59 AM

Originally Posted by starber

1.A car starts from rest and accelerates at 9.50 m/s^2 for 800. m in the eastward direction.
a) How fast is the car going after this? (I got 7.60 x 10^-6 m, but I think I did it way wrong.)

Indeed - if you think about it, there is no way that a car can accelerate like that and only be going 7 micrometers per second. The way to solve this is to use the formula:

$<br /> V_f^2 - V_i^2 = 2 a d<br />$

Here $V_i = 0$ . Calculate $V_f$ .

Originally Posted by starber

b) How long did it take to travel 800. m? (So what I did was I used the formula t = change in velocity / a. But my answer was 800 seconds. Oh geez. )

Once you get the answer to part A correct, you can indeed use $t = \Delta V/a$ to determine the time. Alternatively you could use

$<br /> d = d_0 + v_0 t + \frac 1 2 a t^2<br />$

where $d_0 = v_0 = 0$ . You should try solving this both ways - if you get the same answer that will show that you have done part A correctly.

iangel520 · Sep 24, 2013, 05:41 PM

A subway train starting from rest along a straight track has a uniform acceleration of 1.8 m/s^2 for the first 20 m it travels. Calculate it's speed when it has traveled to 10m

ebaines · Sep 25, 2013, 05:15 AM

Originally Posted by iangel520

calculate it's speed when it has traveled to 10m

You can use the same formula that was discussed in the previous post. Show us your attempt and we'll help if you get stuck.