# Homework Help: Kinematics 2 dimensions problem, golf ball being hit

1. Oct 20, 2011

### jehan4141

A golf ball mass of 4.7 x 10-2 kg is hit by Tiger Woods and drops exactly into a hole 100 meters away. It is observed that the angle between the initial velocity vector and the horizontal plane is 30 degrees.

What is the magnitude of the initial velocity?

Isn't the problem missing additional information? Like time to traverse the 100 meters in the x-direction or the maximum height it reaches??

I don't see how I can solve this problem with additional information.

2. Oct 20, 2011

### SammyS

Staff Emeritus
If the magnitude of the initial velocity is v0, then what is the vertical component, (v0)y, of the initial velocity? What is the horizontal component, (v0)x, of the initial velocity?

What do you know about the horizontal component of velocity during the balls flight?

What do you know about the vertical component of velocity during the balls flight?

3. Oct 20, 2011

### jehan4141

Voy = Vo(sin30)
Vox = Vox(cos30)

I know that the horizontal component doesn't change but that the vertical component does because of gravity....that doesn't help much...? i don't have enough known values.

4. Oct 20, 2011

You do have enough values.

5. Oct 20, 2011

### jehan4141

OHHHH okay oh my...i haven't done 2-d kinematics in a few weeks. thank you i got it. :)

6. Oct 20, 2011

### SammyS

Staff Emeritus
WOW!

I didn't realize how good your hint was until I looked at OP's reply!

Impressive!

7. Oct 20, 2011

### PotentialE

If the ball moved 50 meters horizontally on the first half of its parabolic motion, at an angle of 30 degrees, then use basic trig to find the height it achieved at the peak of the parabola: Tan(30)= x / 50

in the vertical component, you know your acceleration is 9.8(it would be negative but in this case the parabola is symmetric so it doesn't matter) and now you know your distance:
Vf=(2*A*D)^.5
Vf here would be the final velocity on the other side of the parabola, which is the same as the initial velocity on the first side of the parabola (where the ball is struck)
So really, Vi=(2*A*D)^.5

now that you know the upward velocity component and the angle, use trig to find the initial velocity, the hypotenuse: Sin30 = vi/hyp

that gives you your answer, you do have enough information... you just have to take a slightly indirect route

8. Oct 20, 2011

### PeterO

have a play with this:

http://galileo.phys.virginia.edu/classes/109N/more_stuff/Applets/ProjectileMotion/enapplet.html [Broken]

The mass of the projectile makes no difference. You can adjust angle and initial speed.

Last edited by a moderator: May 5, 2017