# Average acceleration issue

1. Jul 10, 2011

### Combine

1. The problem statement, all variables and given/known data
I will just try to post the whole questions, maybe my idiot eyes missed something...

an arrow is accelerated for a displacement of 75cm [fwd]
while it is on the bow, if the arrow leaves the bow at a velocity of 75m/s [fwd]
what is it's average acceleration while it's on the bow

2. Relevant equations
t = displacement/ velocity
a = velocity/time

3. The attempt at a solution

75 cm -> .75
0.75 / 75 = 0.01s
disp = 75m

t = 75/0.75 = 100s
velocity = 75m/s

a = velocity / time
time = displacement + velocity / velocity
acceleration = velocity/(disp/velocity) = vecloity / 0.01 = 7500 WTH!?!?

2. Jul 10, 2011

### SteamKing

Staff Emeritus
The arrow leaves the bow with a velocity of 75 m/s, but its initial velocity = 0 m/s

3. Jul 10, 2011

### Combine

ya it should be, according to logic I guess lol
just i've been having a lot of trouble trying to figure out the average acceleration

4. Jul 10, 2011

### PhanthomJay

Average acceleration is the change in velocity divided by the change in time. You are not given the time. So you must assume a linear variation of acceleration while the arrow is in contact with the bowstring (it behaves like a spring), in which case you can use the standard kinematic equations to solve for the average acceleration.