Calculating Horse Speed: Average Acceleration

[justin32089]

Homework Statement

Running with an initial velocity of 12 m/s, a horse has an average acceleration of -1.79 m/s^2

How long does it take for the horse to decrease its velocity to 7.0m/s ?

Homework Equations

The Attempt at a Solution

ok i got the answer is 2.8 seconds however i got there by adding -1.79 to 12 twice then figuing out the fraction of -1.79 needed to get the velocity down to 7.0.

i was wondering the correct way to do this as it has stumped me
thank you
Justin

 

[gneill]

$$a_{average} = \frac{V_f - V_i}{\Delta t}$$