# Find initial velocity and time in the air- projectile motion

#### dani123

1. The problem statement, all variables and given/known data

A soccer ball is kicked at 38.0° with respect to the horizontal and travels 64.0m before striking the ground.
a) what is its initial velocity?
b) how long was it in the air?

2. Relevant equations

dv=1/2*at2
dh=Vh*Δt
Kinetic equation d=Vi*t+ 1/2*at2
dh=-V2*sin2θ /g
sinθ=opp/hyp
cosθ=adj/hyp
Δt=-2Vsinθ / g

3. The attempt at a solution

a) dh=cos(38)*64m= 50.4m
dv=sin(38)*64m=39.4m

Find t=√(39.4m/(0.5*9.8))=7.96s

plug this value into the d=Vi*t+ 1/2*at2 equation and solve for Vi if d=64m

Vi=3.14m/s

b) V=dh/Δt= 50.4m/7.96s=6.33m/s

Then solve for Δt=-2Vsinθ / g= 0.80s

I would like for someone to just double check my answers and that I used the appropriate equations and that the number of significant figures are being respected! Thanks so much in advance!

Related Introductory Physics Homework News on Phys.org

#### dikmikkel

Sorry, last answer is bad, it looks okay. I would consider the highest y it takes and use energy conservation(kinetic energy) to obtain the initial velocity

Last edited:

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving