impuse question

[tony873004]

3. [Walker2 9.P.014.] A 0.14 kg baseball moves toward home plate with a velocity vi = (-25 m/s) x. After striking the bat, the ball moves vertically upward with a velocity vf = (13 m/s) y.

(a) Find the direction and magnitude of the impulse delivered to the ball by the bat. Assume that the ball and bat are in contact for 1.5 ms.

Don't I need to know what direction the baseball is moving in initially if I am to compute the direction of the impulse. Are they assuming that the ball travels completely horizontal? Or do I not understand this?

[Andrew Mason]

Don't I need to know what direction the baseball is moving in initially if I am to compute the direction of the impulse. Are they assuming that the ball travels completely horizontal? Or do I not understand this?
The impulse is the change in momentum of the baseball. You are to assume that \vec{v_i} is completely horizontal and \vec{v_f} is completely vertical.

Just draw the momentum vectors for the ball before and after the bat hits it. The impulse or change in momentum is the difference between these two vectors (ie. 'what vector added to \vec{v_i} results in \vec{v_f}?'). The impulse is the product of the bat force and the time interval over which it is applied (m\triangle \vec{v} = \vec{F_{bat}}\triangle t).

AM