Running with an initial velocity of 10m/s, a horse has an average acceleration of -1.85m/s2. How long does it take for the horse to decrease its velocity to 6.9m/s ?

Question

parthkohli · Answer

Use the following equation of motion:$$v_i + at = v_f$$Where the symbols are their usual meanings:
$v_i$ is the initial velocity.
$v_f$ is the final velocity.
$a$ is the average acceleration.
$t$ is the time.

anonymous · Answer

So would I just insert all the given variables and get t by itself in order to find the time?? My physics prof. hasn't been super clear in his explaining so he leaves it up to us to figure out.

phi · Answer

yes, fill in the info.  what equation do you get ?

parthkohli · Answer

Follow phi.

You know three of those quantities.  You thus have one unknown quantity, $t$.

anonymous · Answer

(10m/s) + (-1.85m/s^2) t = 6.9m/s would be the equation

parthkohli · Answer

That's right.  The unit of $t$ is seconds, so you cancel that sec out with the sec in the denominator.

anonymous · Answer

So then to the 10 m/s would get added to the 6.9m/s and then divide by -1.85??

phi · Answer

add -10 to both sides

phi · Answer

(10m/s) -10 m/s+  (-1.85m/s^2) t = 6.9m/s  -10 m/s

anonymous · Answer

Then I would add 1.85 to both sides correct??

phi · Answer

no, you said it correctly the first time:
and then divide by -1.85??

anonymous · Answer

1.68 sound right?