Momentum Problem Involving a Falling Plate

[ymartino]

Hey, I need some help with this problem from Kaplan's MCAT Physics review book.

This is a question to a passage and the passage basically says:
A plate is on the edge of a table that is 2m high. The plate falls to the ground and breaks into 3 pieces with the masses 1M, 2M, and 3M. Assume g is 10 m/s^2.

Question:
After the plate breaks, what is the total momentum of all the pieces?
Choices: A.) 720 M m/s
B.) 240 M kg*m/s
C.) 120 M m/s
D.) 120M^2 kg*m/s

(I got the wrong answer because I first solved for the time that it took for the plate to fall, which I used y = 1/2gt^2, and got the answer of 0.2s. Then I used v=at to find the velocity for the plate, which I got 2 m/s. Finally, I used the momentum equation and summed the momentum of each of the plates getting, 6M*v = momentum, in which I got 6M*2m/s, getting 12M m/s. Which is obviously wrong by an order of magnitude. The book explanation somehow gets the time as 2 s which gives the final velocity as 40 m/s. But I don't understand how they get 2m/s unless I am making a really stupid error, which I probably am. Please explain this answer as well as possible. Thanks!)

Correct answer: B) 240 M kg*m/s

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[Cawolf]

No matter how I try it, I get that the velocity when it hits the ground is 6.3 m/s.

The simplest way is the equation that v(d) = sqrt(2gd) = 6.3 m/s

p = mv = (6.3 m/s)(6M) = 38M m/s

Something must be missing here. . . .