Projectile Motion velocity vector Problem

[Lori]

I want to know if i did this problem correctly!

Problem: A projectile is traveling with velocity vector v = (30.00 m/s)i + (20.0 m/s)j when it experiences an acceleration of vector a = (-10.00 m/s^2)j. What is its velocity after 2.0 s? What is its speed after 2.0 s?


My work:

Vy = V0y - gt = 20 - (-10)2 = 40 m/s
Vx = 30 (constant)

Vector v = sqrt( vy^2 +vx^2) = 50
Angle = atan(vy/vx) = 53.13 degrees

Answer:

Speed is 50 m/s
Velcoity is 50 m/s with angle 53.13 degrees


What's the difference between speed and velocity? They are the same except the velocity has direction right?

 

[andrewkirk]

That is all correct.

 

[willem2]

Problem: A projectile is traveling with velocity vector v = (30.00 m/s)i + (20.0 m/s)j when it experiences an acceleration of vector a = (-10.00 m/s^2)j. What is its velocity after 2.0 s? What is its speed after 2.0 s?

My work:
Vy = V0y - gt = 20 - (-10)2 = 40 m/s

why the 2 minus signs for g?

The problem says a = (-10 m/s)j, but you used g = (+10 m/s) j for the acceleration of gravity.
I think a is supposed to be the acceleration of gravity, and you can just use v_y = v_y(0) + a t