Question

problem says that a cannon ball is fired at a 30 degree angle off a 10 meter high wall at 80 m/s. Use work and energy to find it's impact speed.
I worked out this out with the equation:
(1/2)(mass)(initial velocity)^2 + mgy = (1/2)(mass) (final velocity)^2 + mg(y final)
i got impact speed equals 81 m/s. I'm I right?? and if not, were did I go wrong?

Answer 1

initial speed: 80
added energy: mgh=10*9.8*m

total energy= 1/2 m 80^2+98 m
1/2 m vf^2=1/2 m 80^2+98m

vf=sqrt (80^2+98)=80.6m/s

I am not certain how many significant digits you had 10m,80m/s...