Basic kinematics: projectile motion

[Ryaners]

This is a really basic problem but the answers I've gotten don't match up with the back of the book. I've been over it several times & can't understand where I'm going wrong - any pointers would be much appreciated!

1. Homework Statement
A physics book slides off a horizontal tabletop with a speed of 1.40m/s. It strikes the floor in 0.320s. Ignore air resistance. Find a) the height of the tabletop off the floor; b) the horizontal distance from the edge of the table to the point where the book strikes the floor.

Homework Equations

v_f = v_i + at
x = x_i + v_it + ½at²

The Attempt at a Solution

I broke up the book's initial velocity into components:
V_f-x = V_i-x = 1.40m/s
V_f-y = V_i-y +at = -gt = -3.14m/s

The height of the table = the magnitude of the vertical displacement y (using the top of the table as the origin):
y = y_i + V_i-yt + ½at² = 0 + 0 + ½(-9.8m/s²)(0.320s)²= -0.502m -> height = 0.502m
What the book gives for this is 1.13m.

The horizontal distance = magnitude of horizontal displacement x:
x = x_i + V_i-xt + ½at² = 0 + (1.40m/s)(0.320s) + 0 = 0.448m
What the book gives here is 0.502m (which is what I got for the height - which means I'm either completely mixed up or maybe the book is wrong?!)

Thanks for taking a look.

 

[haruspex]

How did you get v_fy=-4.9m/s? Looks like you used t=.5s, which, as it happens, would give a height closer to 1.1m.

 

[Ryaners]

How did you get v_fy=-4.9m/s? Looks like you used t=.5s, which, as it happens, would give a height closer to 1.1m.

Yes, you're right, sorry! I've been trying other problems since getting stuck on this one & copied the wrong figure down from my rough work. It should be V_f-y = -3.136m/s

I'll edit that now.

 

[haruspex]

Yes, you're right, sorry! I've been trying other problems since getting stuck on this one & copied the wrong figure down from my rough work. It should be V_f-y = -3.136m/s

I'll edit that now.

Then I agree with your 0.5m height.