# Homework Help: Projectile motion of car hitting the ground

1. Mar 21, 2013

### Abdeln

1. The problem statement, all variables and given/known data
(Assume no friction) A car that has a mass of 3970 kg is accelerated from an initial velocity of 0 up a ramp that is 50 meters long (the hypotenuse) and has a height above the ground at the end of the ramp of 10 meters. The velocity of the car at the end of the ramp is 150 km/hr. At the end of the ramp the car flies through the air as a projectile. What is the angle of the ramp in degrees? If the car starts up the ramp at time equal to 0 seconds, how many seconds later does the car hit the ground.

2. Relevant equations

3. The attempt at a solution
I know I have to solve for the initial velocities in the x and y direction but I honestly have no idea where to start in this problem--if anyone could just tell me a starting point--it'd be much appreciated.

Last edited by a moderator: Aug 30, 2015
2. Mar 21, 2013

### voko

The angle of the velocity is the angle of the ramp. Which you should determine from the sides given. Recall how the sine is defined.

3. Mar 21, 2013

### Abdeln

I found the angle to be 11.53 degrees, what can I do from there?

4. Mar 21, 2013

### voko

How can you find x and y velocity ccomponents given the sine of the angle and the magnitude of the velocity?

5. Mar 21, 2013

### Abdeln

I don't know. I was never taught that--he gave us a problem set and gave us 2 days to solve it.

6. Mar 21, 2013

### voko

If you knew the x and components of the initial velocity, would you be able to solve the problem?

7. Mar 21, 2013

### Abdeln

I believe so, yes

8. Mar 21, 2013

### voko

Very well. If some velocity has components Vx and Vy, what is the magnitude of the velocity?

9. Mar 21, 2013

### Abdeln

Wouldn't it be the SQRT(Vx^2+Vy^2) ? Using Pythagorean theorem?

10. Mar 21, 2013

### voko

That is correct. The components-magnitude stuff works like sides in a right triangle. So how can you get the components if you know the magnitude ( = hypotenuse) and the angle?

11. Mar 21, 2013

### Abdeln

Oh, just you trigonometric functions and you get the y direction to be 10, and the x direction to be 49?

12. Mar 21, 2013

### voko

These are the sides of the ramp. You need to find the "sides" of velocity.

13. Mar 21, 2013

### Abdeln

knowing that the magnitude of velocity is 150 km/hour?

14. Mar 21, 2013

### voko

Yes.

15. Mar 21, 2013

### Abdeln

ok i changed the magnitude to m/sec to make it easier so it'd be 41.67 m/sec, that'd mean that the x direction it would equal 40.8 m/sec and the y direction would equal 8.3 m/sec. right?

16. Mar 21, 2013

### voko

Correct.

17. Mar 21, 2013

### Abdeln

Would I now plug everything I have into the projectile motion equations?

18. Mar 22, 2013

### voko

Well, you said that given Vx and Vy you should be able to solve the problem. What is difficulty now?

19. Mar 22, 2013

### Abdeln

I was unsure--I managed to solve it.

20. Mar 22, 2013

Good job!