# Help with two 2D motion problems, PLEASE!

1. Aug 28, 2007

### myelevatorbeat

I'm almost done with my homework for the week but I'm stuck on these two questions. I've stated all the work I've done thus far below the problems. Any help would be greatly appreciated!

Problem #1:

A projectile is fired with an initial speed Vo at an angle theta to the horizontal. When it reaches its peak, the projectile has (x,y) coordinates given by (R/2, h) and when it strikes the ground its coordinates are (R, 0), where R is called the horizontal range.

a)Show the projectile reaches a maximum height given by:

h= Vo^2sin^2theta / 2g

b) Show the horizontal range of the projectile is given by:

R=Vo^2sin2theta / g

Problem #2:

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 air is given by y=Ax^2, where A is constant.
b)Express the constant A in terms of the initial (muzzle) velocity and the free-fall acceleration.
c)If x=3.00 m and y=0.210 m, what is the initial speed of the pellet?

I already finished part A and got y(t)= -1/2g[x/(Vo)x)]^2.

Now, I need help starting part B, because I'm completely clueless. I figure I'll just put x and y in part C in the equation I get for part B and that should solve for the last part?

2. Aug 28, 2007

### Mindscrape

Which problem did you get, and which one do you need help with? Can you please put up some work, so we can see how far along you are?