Homework Help: Numerical quantities help

1. Sep 3, 2011

xpaulinabearx

1. The problem statement, all variables and given/known data

K(max) = (6.63x10^-34 J s)(7.09x10^14s) - 2.17x10^-19J
solve for kmax

2. Relevant equations

none?

3. The attempt at a solution
K = (6.63x10^-34 J s)(7.09x10^14 s) - (2.17x10^-19 J)
K = (6.63)(7.09)(10^-34)(10^14) J s^2 - (2.17x10^-19 J)
K = (47.0067)(10^-24) J s^2 - (2.17x10^-19 J)
K = (4.70067x10^-23) J s^2 - (2.17x10^-19 J)
K = J [ (4.70067x10^-23) s^2 - (2.17x10^-19) ]
K = J (10^-19) [ (4.70067x10^-4) s^2 - 2.17 ]

2. Sep 3, 2011

vela

Staff Emeritus
-34+14 = ? (It's not -24.)

3. Sep 3, 2011

xpaulinabearx

oh shoot, stupid mistake! haha, thanks for the catch!

4. Sep 3, 2011

Staff: Mentor

The expression doesn't make sense from the outset: the units being added are not consistent.
(J*s)*s = J*s2, which is not the same as J alone, so these items cannot be added together meaningfully.

Perhaps the first item should be (6.63x10-34 J s-1) ?

5. Sep 3, 2011

vela

Staff Emeritus
The first constant is Planck's constant, which does have units of J s. The second quantity is supposed to be a frequency, with units of s-1. Probably just a typo on the OP's part.