# Calculating the Vertical component of the Velocity

1. Oct 25, 2014

1. The problem statement, all variables and given/known data
A physics class researching projectile motion constructs
a device that can launch a cricket ball. The launching
device is designed so that the ball can be launched at
ground level with an initial velocity of 28.0 m s–1 at an
angle of 30.0 degrees to the horizontal.

2. Relevant equations
Calculate the vertical component of the velocity of the ball:
a initially
b after 1.00 s
c after 2.00 s.
3. The attempt at a solution
Done A how do I do B and C??

Thankyou

2. Oct 25, 2014

### Orodruin

Staff Emeritus
Hi and welcome to Physics Forums!

We require you to show some effort in working towards a solution before we provide help and guidance. What are your own thoughts on how to approach B and C?

3. Oct 25, 2014

I thought about using the acceleration equations though I have not used these before with a degrees in the mix and was unsure if I needed to include this.

4. Oct 25, 2014

### Orodruin

Staff Emeritus
So how do you think the ball is accelerated? Which component of the velocity is affected?

5. Oct 25, 2014

The vertical component because horizontal does not use the acceleration equations

6. Oct 25, 2014

### Orodruin

Staff Emeritus
Yes, so try applying that and show us what you get.

7. Oct 25, 2014

so using the initial vertical component at the initial velocity in the equation v=u+at?

8. Oct 25, 2014

### Orodruin

Staff Emeritus
Yes. As you said yourself, this is the only component of velocity that is influenced by the acceleration.

9. Oct 25, 2014

Thankyou!!! Now I have it is seems easy! just wondering, why is the 9.8 ms-2 negative? is is because when it is moving up it is going in the opposite direction? If so does this mean that when is is moving downwards the 9.8ms-2 would be positive?

10. Oct 25, 2014

### Orodruin

Staff Emeritus
This depends completely on how you have defined your coordinates. If you have defined the up direction as the positive y-direction, then the gravitational acceleration will be in the negative y-direction, i.e., down. If you did it the other way around and defined the down direction as positive, then you would have a positive gravitational acceleration, but the sign of the initial velocity in that direction would be changed as well.