- #1

Ryang

- 6

- 0

## Homework Statement

To Find initial velocity, given final velocity, and displacement on Y axis.

Hello. I've spent four hours trying different solutions to this following problem, none of which have worked. I've just started my undenominated science degree, and since I havn't started lectures yet I've worked ahead in my physics book, to avoid getting stuck later on in the year. Help with workings would be much appreciated.

**Given:**

"an baseball has velocity of 36 m/s, at an angle of 28 from the horizontal (x axis). The positive directions are to the right of the horizontal, and the top of the vertical axis. Ignoring air resistance, find the magnitude and direction of the initial velocity of the object."

- The objects final position is displaced +7.5 metres on the Y axis from its original position. -- Final velocity is 36 m/s, 28 degrees down from the horizontal.

- Acceleration on the X axis is obviously = 0m/s

- Acceleration on the Y axis is = -9.80 m/s

**Unknown**

The Unknown variables are the:

Magnitude of initial velocity.

Direction of initial velocity.

## Homework Equations

These are the equations I imagine are relevant.

**Initial Velocity**

Magnitude = V

_{o}= √V

_{ox}

^{2}+ V

_{oy}

^{2}

Direction = Theta = Tan inverse (V

_{oy}/V

_{ox})

## The Attempt at a Solution

Sorry, I'm not great with using the mathmatical symbols on this board. I'll do my best.

V = 36m/s

Vx and Vy form a right angle triangle to V.

36/Sin 90 = V

_{y}/ Sin 28

36 m/s (Sin 28) = V

_{y }

Vy = 16.90

36

^{2}= 16.9

^{2}+ 19.1

^{2}

Vx = √19.1 = 4.37

- - - - - - - - - - - -

To find V

_{oy}, I tried

_{oy}= + √(-36 sin 28)

^{2}- 2 (-9.80)(7.5) = 20.8

V

_{oy}= 20.80 m/s

V

_{ox}= 4.37 m/s

- - - - -- - - - - - - - - - - -

**Problem:**

using pythagorases theorum for a right triangle, I found that the velocity V

_{0}was = 21.25, but my book says that the magnitude for the velocity should be:

38m/s

Where am I going wrong?? I would really appreciate help, very sorry if I didn't provide sufficient workings but I think I did. And sorry if my inevitably idiotic error is frustrating for you to see, I'm not very mathematically inclined, which is the reason I'm practicing so much. Thanks

Ryan

Last edited: