Question

What is the speed of the projectile immediately before it hits the ground?

Answer 1

✓2gh. this the possibly right answer....................

Answer 2

(a) the initial total mechanical energy of the projectile 
= 0.5 *60 * 124^2 
= 461280 J --answer 

(b) Suppose the projectile is traveling 87.9 m/s at its maximum height of y = 314 m. 
height travelled = 314 - 154 = 160m 
PE = 60 * 9.81 * 160 = 94176 J 
KE = 0.5 * 60 * 87.9^2 = 231792.3 J 

work has been done on the projectile by air friction 
= 461280 - 94176 - 231792.3 
= 135311.7 J ----answer 

(c) if air friction does one and a half times as much work on the projectile when it is going down as it did when it was going up
work done by friction = 1.5 * 135311.7 J = 202967.55 J 

PE lost = 60 * 9.81 * 314 = 184820.4J 
KE gain = 0.5 * 60 * v^2 

461280 = 202967.55 + 184820.4 + 0.5 * 60 * v^2 
v =49.49 m/s 
answer 

speed of the projectile immediately before it hits the ground