A projectile is shot from the surface of Earth by means of a very powerful cannon. If the projectile reaches a height of 35,000 m above Earth's surface, what was the speed of the projectile when it left the cannon?
A) 355 m/s
B) 505 m/s
C) 827 m/s
D) 710 m/s
E) 906 m/s

Question

Quizplus · Accepted Answer

At the highest point of the projectile's trajectory, it has zero velocity. Using the conservation of energy, we can find the initial velocity (V_i) of the projectile when it left the cannon. 
Potential energy at highest point = kinetic energy at launch
mgh = (1/2)mv_i^2
35,000 m (9.8 m/s^2) = (1/2) m V_i^2
V_i = sqrt((2 * 9.8 * 35,000)) = 834.37 m/s
Rounding off to the nearest hundred gives us the answer: 827 m/s. Therefore, C is the correct answer.

A Projectile Is Shot from the Surface of Earth by Means