Calculating Final Position in Projectile Motion: A Case Study

[NoMeGusta]

I just wanted a second check on this. This is a mortar fired at a mountain to cause an avalanche. What is xf and yf given:

Vi=300 m/s
theta= 55 degrees
t = 42 secs

so I found
Vxi= 300cos(55) = 172 m/s
Vyi= 300sin(55) = 245 m/s

Xf = Xi +Vxi*t + (1/2) ax*(t^2)
= 0 +172(45) + (1/2)(0)(45^2)
= 7227 m
= 7.23 X 10^3 (this was correct w/the book)

Now for Yf
Yf = Yi +Vyi*t + (1/2) ay*(t^2)
= 0 + 245(45) + (1/2) (-9.80)*(45^2)
= 11058 - 9922
= 1136
= 1.14 X 10^3 ... book says 1.68 X 10^3

What am I doing wrong to not get Yf correct? Thanks for the help.

 

[Chi Meson]

what's t? 42 or 45 s?

 

[NoMeGusta]

Oh shoot, it is 42, but for some stupid reason I wrote 45 in finding Yf. I redid it with t=42 and I got the right answer, woohoo, thanks!