# Height of an object

1. Feb 4, 2009

### chrisridgwell

a wheel becomes detached from a race car, the wheel is travelling at 45m/s at an angle of 35 deg. a fence is erected 25m from the track. ignoring air resistance how high should the fence be?

gravity 9.8

ive tried drawing a diagram, with angle of 35 deg. i believe it is a trig question

2. Feb 4, 2009

### Kurdt

Staff Emeritus
3. Feb 4, 2009

### chrisridgwell

see that doesnt make any sense to me!!

4. Feb 4, 2009

### Kurdt

Staff Emeritus
What will be the vertical and horizontal components of velocity using trig?

5. Feb 4, 2009

### chrisridgwell

see thats where im stuck i need to know how to calculate this:
if i know the angle and the adjacent,
35 deg, 25m and i want to the height, opposite, 35 x 25 as in Tan x adj

6. Feb 4, 2009

### Kurdt

Staff Emeritus
Ahh I see. You misunderstand slightly, its not assimple as that. The wheel does not travel in a straight line since it is subject to gravity and that is why you need to use kinematic equations. You use trig to find the components of the velocity vector (i.e. the magnitude of the velocity is the hypotenuse of a right angled triangle). The components tell you the horizontal and vertical velocity of the wheel to which you can apply the kinematic equations.

7. Feb 4, 2009

### chrisridgwell

i was lead to believe it would travel in a straight line as its travelling at 45m/s and the fence is only 25m away

8. Feb 4, 2009

### Kurdt

Staff Emeritus
By who? If that is the case why were you given the gravitational acceleration of g?

9. Feb 4, 2009

### chrisridgwell

sorry if i have confused it, this is an assignment question which i got late as i missed a lesson
the question says that the wheel is travelling at 45m/s at 35 deg. the fence is 25m away, how high does it have to be to prevent it hitting the crowd. then in brackets it just says take gravitational field strength to be 9.8 N/kg

10. Feb 4, 2009

### Kurdt

Staff Emeritus
The you will definitely need to take gravity into account. So begin by finding the components of the wheels velocity and then use the appropriate kinematic equations to see how high the wheel will be when it reaches the fence.

11. Feb 4, 2009

### chrisridgwell

what do you mean by components? im sorry im new to physics

12. Feb 4, 2009

### Kurdt

Staff Emeritus
Like I said previously consider the vector as the hypotenuse of a right angled triangle. The other two sides of the triangle will then be the components of the vector which you can work out using trigonometry. Read the following page for more information on vectors in general including resolving components.

http://hyperphysics.phy-astr.gsu.edu/hbase/vect.html

13. Feb 4, 2009

### chrisridgwell

im stuck now, as the horizontal is flat so it is at 0 degress, and i cant calculate the other side as i dont have the information to.

14. Feb 4, 2009

### Kurdt

Staff Emeritus
Both sides can be calculated from the hypotenuse and the angle. Did you read the link I gave you about resolving components? Its just the same as calculating the length of sides of a right-angled triangle in trigonometry class.