# Homework Help: Finding Time with 3 unknowns

1. Sep 20, 2009

### Rubix

3rd week in AP physics... can't figure this out :'(

1. The problem statement, all variables and given/known data
delta X = 20m
delta Y = -1.5m
angle = 10 degrees

basically, a car goes off a 10 degree ramp and lands 20 meters away and the delta Y is 1.5m... my assumption is that I need to find T first.

2. Relevant equations
we are given 4 equations:
delta X = VxoT
Vy = Vyo + AyT
delta Y = VyoT + (1/2)AyT^2
Vy^2 = Vyo^2 + 2Ay(delta Ymax)

3. The attempt at a solution
i have no attempt.

2. Sep 20, 2009

### rock.freak667

y=y0+vxt-1/2gt2

you want to find t when y=0 (y0=1.5)

3. Sep 20, 2009

### Rubix

I don't know what Vx is.

4. Sep 20, 2009

### rock.freak667

the angle θ=10

so vx=vcosθ

and vy=vsinθ

Also I made a typo,the equation should be

$$y=y_0 +v_y t -\frac{1}{2}gt^2$$

(not vx in it)

5. Sep 20, 2009

### Anden

A hint: You must plug one equation into another on this one, this will result in the removal of Vo from an equation and leaving only time.

6. Sep 20, 2009

### Rubix

I still need help, I know i need to plug in equations into each other but i'm not sure which ones

7. Sep 20, 2009

### Rubix

figured it out, the key was

t = (20.33/v)

then i plugged that into this eqn:

delta X = VxoT