# Homework Help: Projectile motion

1. Jun 11, 2010

### Trandall

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

A ball is thrown at a velocity of 10 m/s, at an angle of 30° from horizontal and released 2 m
above the ground. What will the magnitude of ball’s resultant velocity be at the moment of
impact with the ground?

2. Relevant equations
Vf2 = vi2 + 2as

3. The attempt at a solution

Vf2 = 5(2) + 2 x -9.8 x -2
Vf2 = 25 + 39.2
Then find the square root

The answer is 11.8 m/s

Thanks

2. Jun 11, 2010

### rock.freak667

Split the velocity into components.

Use v2=u2-2g(s-s0) to find the vertical component of velocity when it hits the ground.

3. Jun 11, 2010

### Trandall

Im sorry, im still stuck, could you write it out in the formulae, Im clueless when it comes to physics.

4. Jun 11, 2010

### rock.freak667

v2=u2-2g(s-s0)

v= final velocity
u= initial velocity
g= acceleration due to gravity
s= displacement
s0=initial displacement

5. Jun 11, 2010

### graphene

you'll have to analyze motions in the x & y direction separately as acceleration is along the y direction only.

X
${v}_{x0} = 10 \cos 30$
${a}_{x} = 0$
${v}_{x} = {v}_{x0}$

Y
${v}_{y0} = 10 \sin 30$
${a}_{y} = -g$
${s}_{y} = -2$

${s}_{y} = {v}_{y0}t + \frac{1}{2}{a}_{y}{t}^{2}$
solve for t & then use -
${v}_{y} = {v}_{y0} + {a}_{y}t$

6. Jun 11, 2010

### Trandall

Thanks heaps for your help =)