# Projectile being launched off a table at an angle?

1. Feb 18, 2014

### megmar95

1. The problem statement, all variables and given/known data

We did an experiment where we launched a ball off a table at an initial velocity of 1.80 m/s, at an angle of 10 degrees. We measured the distance in the x-axis the ball travelled 0.743 m. Using this information, we are supposed to calculate a predicted value for the distance in the y-axis (initial height). Since we did the experiment, we have an experimental value of 1.12 m for the height, but my teacher wants us to calculate a predicted value for initial height and compare using absolute % error ((predicted - experimental) / experimental).

2. Relevant equations

vix = (vi)cos(10)
vfy=(vi)sin(10)
ax = 0
ay= -9.81
t = ?
dx= 0.743 m
dy = ?
3. The attempt at a solution

I calculated vix to be 1.773 m/s and viy to be 0.3125667 m/s. I'm unsure how to calculate time, and also am unsure if there is a vi for y-axis (my teacher said I did the question wrong because I used dy= vit + 1/2at^2 and cancelled out vit because I believed vi was 0 but the ball is being launched so there is a vi for y).

2. Feb 18, 2014

### voko

The equation you used wrongly is OK, just use it correctly. Since $v_{iy}$ is not zero, as you said, do not set it to zero.

3. Feb 18, 2014

### tiny-tim

hi megmar95! welcome to pf!
the initial height is zero

do you mean maximum height?

(and is the table flat? and is the ball landing on the table again, or on the floor?)
yes, vi is at an angle, so viy = visin10°

4. Feb 18, 2014

### megmar95

Ya I meant the distance travelled by the ball in the y-axis altogether (range)
The ball was launched off the end of a ramp angled at 10 degrees placed on top of a flat table at the very edge of it, and landed on the floor.
I tried using the (vi)sin(10) and plugged it into the equation d=vit+1/2at^2, so d= (0.3125)(0.419) + 1/2(9.81)(0.419)^2 and I got an answer of 0.992 m for predicted height. Afterwards I used the % error equation, and got a percent error of 11.4%, does that sound correct?