Projectile physics?

Question

A projectile of mass 7.4 kg kg is shot horizon-
tally with an initial speed of 19.5 m/s from a
height of 20.6 m above a flat desert surface.
The acceleration of gravity is 9.81 m/s2 .

a) For the instant before the projectile hits
the surface, find the work done on the projec-
tile by gravity. Answer in units of J.

Find the change in kinetic energy since the
projectile was fired. Answer in units of J.

Find the final kinetic energy of the projec-
tile. Answer in units of J.

Answer 1

b) That's the potential energy

c) That's the potential energy added to the initial kinetic energy of the projectile

Answer 2

I don't have a calculator so you can do that part but you set it up like this.

First find the time the projectile is in the air. d=1/2 a t squared so the a or acceleration is 9.8 the d or distance is 20.6 and the t is what you are solving for so t= the square root of 41.2 divided by 9.8.

Now you know the time so you can multiply the prev. answer times 19.5. Than take that number and use the work formula work equals force times distance. You know the distance from the previous calculation and you know that f=ma so 7.4 times 9.81 times your previous answer will give you the answer for part a.

Answer 3

1493 J for all. ( 1500 J if you want sig.figs. )