The formula for half-life is:

Where A is the amount of iodine-131 initially and after 40 days, t is time, h is half-life of the isotope. Let's plug in our values to the equation:

Therefore, the patient has 0.625 grams of iodine-131 after 40 days.
Answer:
B. A system cannot take in additional matter.
Explanation: The total amount of energy in the universe remains constant, it can merely change from one form to another.
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B. The apple from the bottom will hit the ground earlier. This is because an increase in height causes an increase in the time that the object will fall, and therefore will affect the final velocity of the falling object. Moreover, the reduction in velocity due to friction from the air should also be considered.
Answer:
Find the time it took for the car to stop at 11.0m/s
V = deltax/t
t = 41.14/11.0 = 3.74s
Now find at what rate it was decelerating, so find the acceleration during that interval of time.
vf = vi + at
-11.0m/s = a3.74s
a = -2.94m/s^2
The acceleration is negative because is pulling the car towards its opposite direction to make it stop.
Now find how much time it would take for the car to stop at 28.0m/s but with the same acceleration, the car is the same so its acceleration to stop the car will remain the same.
vf = vi + at
0 = 28.0 - 2.94t
t = 9.52
Once the time is obtained, you can find the final position, xf, by plugging the time acceleration and velocity values.
xf = 0 + (28m/s)(9.52s) + 1/2(-2.94)(9.52s)^2
xf = 266.6m - 133.23m = 133m
At the "very top" of the ball's path, there's a tiny instant when the ball
is changing from "going up" to "going down". At that exact tiny instant,
its vertical speed is zero.
You can't go from "rising" to "falling" without passing through "zero vertical
speed", at least for an instant. It makes sense, and it feels right, but that's
not good enough in real Math. There's a big, serious, important formal law
in Calculus that says it. I think Newton may have been the one to prove it,
and it's named for him.
By the way ... it doesn't matter what the football's launch angle was,
or how hard it was kicked, or what its speed was off the punter's toe,
or how high it went, or what color it is, or who it belongs to, or even
whether it's full to the correct regulation air pressure. Its vertical speed
is still zero at the very top of its path, as it's turning around and starting
to fall.