Calculating BB Gun Muzzle Velocity Using Projectile Motion Equations

[blackboy]

Homework Statement

A student decides to measure the muzzle velocity of a pellet shot from his gun. He points the gun horizontally. He places a target on a vertical wall a distance x away from the gun. The pellet hits the target a vertical distance y below the gun.
(a) Show that the position of the pellet when traveling through the air is given by y = Ax^2, where A is a constant.
(b) Express the constant A in terms of the initial velocity v and the free-fall acceleration g.
(c) If x = 3 m and y = 0.21 m, what is the initial speed of the pellet?

Homework Equations

The Attempt at a Solution

Can I assume vi is constant? For (a) I got y=x^2[g/(2vi^2)]. Is vi a constant? If so then I know to do it. If not can you help? Thanks.

 

[PhanthomJay]

The initial velocity is of a given magnitude and direction. While instantaneous velocity might change, the initial velocity is just a constant. Your equation, however, is almost correct, but not quite.

 

[blackboy]

Hmm I tried it over and I still get the same answer. What did I do wrong?

 

[PhanthomJay]

O,so sorry, you are correct, I was reading your equation incorrectly.

 

[blackboy]

Ok thanks for your help.