# Homework Help: Velocity help Vf vs. Vx

1. Dec 7, 2004

### JWest

Which way is closer to the actually velocity of a car rolling down a ramp and falling off a desk to the floor? Finding the final velocity (Vf) or finding the horizontal velocity (Vx)? Why?

2. Dec 7, 2004

### ceptimus

You really need to calculate the horizontal velocity component Vx, and the vertical velocity component Vy, then you can combine the two together to get the final velocity you call Vf. You can draw a right angled triangle with Vx and Vy as the two shorter sides, and Vf will be the length of the hypotenuse.

Now I don't have the diagram, so I'm not sure how the ramp is placed on the desk. Is the ramp right on the edge of the table, so the car is still going down it before it falls, or is there a length of flat table after the ramp, before the car falls off?

If there is some flat horizontal table between the ramp and the edge, then you know that the car's initial downward velocity Vy is zero, and its final downward velocity will just be due to the fall from the height of the table. If the car is still going down the ramp, you need to figure how fast it's going across and down, as it comes off the end.

Either way, once the car is clear of the table, its horizontal velocity Vx won't change, and only Vy will increase due to the force of gravity.