physics
posted by bec .
a boy stands on a cliff overlooking a lake below. He throws a rock at an initial velocity of 8.0m/s,at an angle 25 degrees above the horizontal. The lake's surface is 4.5 m lower than the point the rock was released. Find the speed of the rock just before it hits the surface of the water. Ignore air friction.

final KE= Initial KE+ initial PE
1/2 mvf^2=1/2m(8)^2 + m*9.8*4.5
solve for Vf 
can i do this with out m?
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