Answer:
a) 0.0288 grams
b) 
Explanation:
Given that:
A typical human body contains about 3.0 grams of Potassium per kilogram of body mass
The abundance for the three isotopes are:
Potassium-39, Potassium-40, and Potassium-41 with abundances are 93.26%, 0.012% and 6.728% respectively.
a)
Thus; a person with a mass of 80 kg will posses = 80 × 3 = 240 grams of potassium.
However, the amount of potassium that is present in such person is :
0.012% × 240 grams
= 0.012/100 × 240 grams
= 0.0288 grams
b)
the effective dose (in Sieverts) per year due to Potassium-40 in an 80- kg body is calculate as follows:
First the Dose in (Gy) = 
= 
= 
Effective dose (Sv) = RBE × Dose in Gy
Effective dose (Sv) = 
Effective dose (Sv) = 
Answer:
The average speed of 3.5 m/s means that it takes Sally approximately 47.619 minutes to run 10,000 meters
Explanation:
Average speed is a scalar quantity that is given by dividing the total distance moved or traveled by an object by the time that it takes the object during the motion
The average peed indicates the rate at which the object makes a given amount of journey distance given that the journey is completed with varying speeds
With the knowledge of the average speed and the distance covered, the time for completion of the journey can be found as follows;

Where
= Average speed of the object = 3.5 m/s
Δt = The time it takes the Sally to run 10,000 meters
Δx = The total distance Sally runs = 10,000 meters
Therefore;

The time it takes the Sally to run 10,000 meters= Δt = 20,000/7 seconds ≈ 2,857.143 seconds
20,000/7 seconds ≈ 47.619 minutes
Therefore, the average speed of 3.5 m/s means that the time it takes the Sally to run 10,000 meters ≈ 47.619 minutes
Answer:
Because they are moving to fast for Earth's gravity to pull it down.