# Velocity problem determining x and y components

1. Sep 18, 2012

### brandon133

An object undergoing parabolic motion travels 100 m in the horizontal direction before returning to its initial height. If the object is thrown initially at a 30° angle, determine the x component and the y component of the initial velocity. (Neglect any effects due to air resistance.)

I am not sure how to go about solving... I got an initial vector from the throw but I dont think it can be the initial velocity vector since I have no judgment of time.. could someone show me the process of solving this?

2. Sep 18, 2012

### HallsofIvy

Staff Emeritus
If we let "$v_x$" and "$v_y$" be the components of velocity in the x and y directions, respectively, then $x= v_xt$ and $y= -4.9t^2+ v_yt$ so we have $y= -4.9t^2+ v_yt= 0$ (the projectile hits the ground) and $x= v_xt= 100$ (the projectile hits the groud after 100 m). The fact that "the object is thrown initially at a 30° angle" means that $v_y/v_x= tan(30)$. That gives you three equations to solve for the three values, t, $v_x$, and $v_y$.

3. Sep 18, 2012

### rl.bhat

If vsinθ is the y component of the velocity, what is the time the projectile takes to return to its Initial height?
If vcosθ is the x component of the velocity, what is the expression for the range x?

4. Sep 18, 2012

### azizlwl

The time taken for the object to travel horizontally 10m is equal to the time taken from launching up and back to same level.

It is a single body, at same place(different x and y coordinates) and at same time.