Calculating Change in Velocity for a Baseball Player's Slide

[Evales]

The following diagram shows the path taken by the center of mass of a baseball player sliding along the ground in an attempt to make the base.

The player is moving at a speed of 10m/s just before the slide and his speed 0.5 seconds later is 8.0m/s. The mass of the player is 80kg

1a) Calculate the magnitude of his change in velocity during this 0.5second interval.
b) Calculate the average acceleration during the 0.5 second interval.

My answer:
cos20 = a/8
a = 7.52

10 - a = 2.48

Therefore the change in velocity is 2.48m/s

The actual answer:

3.7m/s

How do you do this kind of question?

 

[Kurdt]

Velocity is a vector so if you set up a coordinate system you can find the velocity change and then the magnitude more easily.

 

[Evales]

What do you mean? I tried tried solving it as a vector. How should I tackle this?

 

[Kurdt]

In you calculation you've only found one component.

 

[Evales]

That is true but the answer too has only one component. Finding the change in direction won't make my answer 3.7m/s ??

 

[Kurdt]

Yes but the answer is the magnitude of a vector (i.e. its length).

 

[Evales]

Thanks! I got it. I couldn't quite understand what you meant. Sorry, you meant vector subtraction right??

Thanks a bunch : )