# Homework Help: Projectile Motion of spear throw

1. Feb 10, 2017

### iwan97

1. The problem statement, all variables and given/known data
Man is throwing a spear at distance of 100m away from a building. Window is at the height of 50m. At which angle and velocity man has to throw spear? Spear must be parallel to ground when going through a window.

I can figure out this one. I usually first calculate time in the air but it doesn't work in this one.

I split all data and variables in horizontal and vertical direction so it would be something like this:

Horizontal

x0=0m
x=100m
a=0m/s2
vox=cosα*v0

Vertical

y0=0m
y=50m
a=-9.81m/s2
v0y=sinαv0

2. May 19, 2017

### Mr Real

This is quite late but i'm still posting my answer: In this question range and maximum height of the projectile are already given. To get the angle, you can do this by finding the relation between range and maximum height, which is: range is twice of maximum height.Solving the relation, you would get the angle. To find initial velocity, you just need to apply the formula of either range or maximum height.
p.s. It's my first actual answer on this forum. Hope it helped☺.

3. May 19, 2017

### iwan97

3 months late mate :)
I found the answer my self but thanks for posint anyways!

4. May 19, 2017

### CWatters

The management actually encourages people to answer as many unanswered questions as possible even if late because they still show up in searches. Over 120 people viewed this thread since it was originally posted.