Calculate Horse Motion Problem: Vavg & Velocity

[kp87]

A horse canters away from its trainer in a straight line, moving 140 m away in 10.0 s. It then turns abruptly and gallops halfway back in 4.9 s.

(a) Calculate its average speed.
(b) Calculate its average velocity for the entire trip, using "away from the trainer" as the positive direction.

I got a right by Vavg=(V+Vo)/2 [(140/10)+(70/4.9)]/2 and got 14.14 m/s.
so I was thinking that for part B it would be [(140/10)-(70/4.9)]/2 and got -.143... and it is wrong...

can anyone help me?

 

[AngeloG]

First of all ask yourself these questions: "What is an average speed?" Speed is not a vector, it's a magnitude =). What two variables does it depend on? The second asks for the average velocity for the entire trip meaning it's a vector.

Think about these and it should come a little bit more clearly.

 

[kp87]

thx a lot :0