An airplane is flying at a rate of 100km/h north. Inside of the airplane I throw a ball at a speed of 50km/h. What is the relative velocity?
a) towards the front of the plane?
b) towards the back of the plane?

answers:
oubaas say: if the object is thrown vertically :
Vox = 100 km/h
Voy = 50 km/h
Vo = 50√1+2^2 = 50√5 km/h
relative velocity is just the vector difference i.e. 50 km/h for both front and back

electron1 say: Toward the front of the plane, the relative velocity is 50 km/h. Toward the back of the plane, the relative velocity is 150 km/h.

Vaman say: You are stationary with respect to the airplane so all others. Therefore, all will see 50 km/h velocity.

Tom S say: Which direction are you throwing the ball? That is important to know.

derfram say: Relative to what? To someone standing on the ground, then refer to billrussell42's answer. To someone in the airplane, 50 km/h.

Demiurge42 say: Assuming the plane's velocity is relative to the ground and the ball's speed is relative to the plane then you can figure out the ball's velocity relative to the ground be adding the velocities of the plane relative to the ground and the ball relative to the plane.
Let North be the positive direction.
a)The plane has a velocity of 100km/h. The ball has a velocity of 50km/h relative to the plane. The sum is 150km/h. The ball has a velocity of 150km/h relative to the ground.
b)The plane has a velocity of 100km/h. The ball has a velocity of 50km/h relative to the plane. The sum is 50km/h. The ball has a velocity of 50km/h relative to the ground.

billrussell42 say: if you throw it towards the front, the velocities add.
towards the rear, they subtract.
