- #1
Medgirl314
- 561
- 2
Homework Statement
An arrow is fired from the top of a 60 m high cliff. It is fired at 80 m/s at a 30 degree angle above horizontal.
a)Find the time of the arrow's flight from start to impact.
b)Find the horizontal distance the arrow travels.
c)Find the velocity of the arrow(magnitude and direction) when it strikes the ground.
2. Homework Equations
sine
cosine
x=vt
t=(v-v0)/a
3. The Attempt at a Solution
a)
I calculated the vertical and horizontal velocities.
Horizontal: 80 cos 30= 69.8 m/s
Vertical:80 sine 30= 40 m/s
Then I calculated the time.
v0=40 m/s
a=-9.8 m/s^2
v=0
t=(v-v0)/a
t=(0-40)/-9.8
t=4.1
This was considering the time from start to peak, so we double to get 8.2 s.
b) x=vt
x=69.28(58.2)
x=4032 m.
This seems conceivable, but not exactly right.
c) How do I find the magnitude and direction? It is lost on me at the moment. If the arrow is *on* the ground, it's not moving, and so the velocity would be 0 m/s. But I am assuming the question means the velocity at the exact moment it hits the ground.
We aren't taking air resistance into account.
Thanks in advance!
I posted this problem previously, and was told to try this equation for the time instead: y=y0+v0t+1/2a*(t^2).
I did, and got this far:
2y=2y0+2v0t+a*t^2
120=0+2(69.8 m/s*t)+9.8 m/s^2(t^2)
But I suppose the other users grew tired of helping me and left. Would someone mind picking it back up? I have worked for at least an hour now on these problems, and I get the concept, but I do need help with some of the steps.
Thanks so much!