Projectile Motion trajectory Problem

[mst3kjunkie]

8. A Physics student on Planet Exidor throws a ball, and it follows the parabolic trajectory shown in Figure 6.8 (whille it will not be recreated on this forum, the figure shows a part of a parabolic curve which starts at the origin and peaks at t=2. It also shows the velocity vector at t=1, which will be entered later in the pst). The ball's position is shown at 1 s intervals until t=3s. At t=1 s, the ball's velocity is (2.0i + 2.0j)m/s, where i and j are unit vectors.

a. determine the ball's velocity at t=0,2,and 3 s.
b. what is the value of g on planet Exidor?
c. what was the ball's launch angle.

I know how to do parts b and c, but can't do either without a. I'm not sure what formula to use, but I do know the following:

at t=1:
v1=(2.0i + 2.0j)m/s
v1x=2.0im/s
v1y=2.0jm/s

ax=0
ay=-g m/s^2

v1x=v0x=v2x=v3x2.0im/s
x0=0m
y0=0m

Thank you in advance.

 

[Doc Al]

Treat the vertical and horizontal components separately. Hints: What's the vertical component of velocity at the highest point? (t = 2) What about the horizontal component?

 

[mst3kjunkie]

Figured it out. since the velocity in the y direction is 0m/s at t=2s, I was able to calculate the gravity. I then used this to find the velocities at the other times. I don't know if using part b to solve part a is correct, but I can check my instructor's webpage to see if it gets the correct answer.