I got A but what does B mean and how do i do it?

Question

8). A ball is projected horizontally from the edge of a table that is 1.00 m high, and it strikes the floor at point 1.20 m from the base of the table. (a) what is the intial speed of the ball? (b) How high is the ball above the floor when its velocity vector makes a 45 degree angle with the horizontal?


I found A to be 2. 67 m/s ... I dont get and don't know how to do B ... Help

Answer 1

B = .25 m

Answer 2

The ball is 0.636m above the floor

In order for the velocity vector to be at 45 degrees the horizontal velocity must equal the vertical velocity.
2.67m/s = vhoriz = vvert = g*t
t=2.67/g
then
height = 1m - vertical distance
height = 1m - 1/2 * g * t^2
= 1m - 1/2 * g (2.67/g)^2
= .636 m

Answer 3

To solve (b) you must note that sin45 = cos45, so the magnitude of the horizontal component of velocity must equal the magnitude of the vertical velocity:

v^2 - 0 = 2as
s = (v^2)/2a
s = 2.67^2)/(2*9.8) = 0.364 m from the table top, or 0.636 above the floor.

Answer 4

.2 m

Answer 5

Calculus works exceptionally in this instance for b. all you have to do is use the equation you get for the projectile motion take its derivative and evaluate that deriveative at 1/2 the time