# Vector/Relative Motion Questions

1. Sep 23, 2013

### zak.hja

1. The problem statement, all variables and given/known data
A boy rides his bicycle down the sidewalk at a velocity of 0.50 m/s [N]. As he passes his friend, who is 5.0m east of his position, he throws a ball to him.

a) If he can throw the ball at a maximum velocity of 2.0m/s, in which direction must he throw it in order for it to reach his friend?

b)How long does it take the ball to reach his friend?

2. Relevant equations

c^2=a^2+b^2

3. The attempt at a solution

Well, I know that a right triangle can be formed with the vectors. We've just started this topic today, so I'm a bit unsure of where to put the numbers. One side of the triangle will be 0.5 m/s in magnitude, and another will be 2.0 m/s. How would this triangle look?

Any assistance is appreciated; thank you :)

2. Sep 23, 2013

### Simon Bridge

Do you know how to do it if the target is moving?

You need to think through the physics without worrying, right away, about the "right way" to do this thing.

Without air resistance[*], if the bio just let go of the ball, what speed and direction would it travel? How fast?
You need the ball to go directly in what direction?

So the direction you throw it must cancel out all the directions you don't want it to go in.

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[*] or gravity apparently - we'll treat the 2.0m/s as the horizontal velocity, the boy adjusts the vertical velocity to suit. (You'll probably do projectile motion later.)

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