Answer:
1280 mg
Explanation:
Radioactive decay is a phenomenon that occurs when a certain isotope of an element, said to be radioactive, decays, turning into a lighter nucleus and emitting radiation + energy in the process.
The radioactive decay of this isotope of polonium is described by the equation

where
is the amount of polonium left after time t
is the amount of polonium t time t = 0
is the half-life of the polonium, in days (it is the time it takes for the initial element to halve its amount)
IN this problem, we know that:
After t = 560 days, the amount of polonium left is
. Therefore, we can re-arrange the equation, substituting t = 560 d, and solve for
to find the initial amount of polonium:

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Hope I helped!
Answer:
The magnitude of the average angular acceleration is calculated as 
Explanation:
Maximum speed that can be attained by the disk,
= 10,000 rpm
Speed of spinning of the disk, N = 7570 rpm
Time taken to come to rest, t = 0.435 s
Now,
The initial angular velocity is given by:

Final angular velocity, 
The average angular acceleration of the disk can be computed by using the kinematic eqn:



Potassium is the 19th element so it is B
While pushing a refrigerator up a ramp, there would be less friction to overcome if you used a dolly because of the wheels. So the efficiency of the ramp would be greater with the use of the dolly.
<u>Explanation:</u>
The ramp provides for a wedge setup, so when the refrigerator is being pushed up the ramp, the friction on the ramp would equally distributed to the refrigerator when pushed wholly as the friction applied is a product of the coefficient of friction with the Normal reaction of the weight in contact with the surface.
Therefore, when the dolly is used, the surface in contact becomes divided and thus, the friction applied would become less due to though coefficient of friction remains the same, the normal reaction of the weight becomes small and so does the applied friction. Therefore, efficiency of the ramp increases as the friction is less and work done is more.