1) The half-life is the time required for a substance to reduce to half its initial value. In formulas:

(1)
where
m(t) is the amount of substance left at time t
m0 is the initial mass

is the half-life
In this problem, the half-life of the substance is 20 years:

therefore, the fraction of sample left after t=40 years will be

So, only 1/4 of the original sample will be left, which corresponds to 25%.
2) We can use again formula (1), by re-arranging it:

If we use m(t)=10 g (mass of uranium left at time t), and

(the time is equal to 4 half lifes), we get

So, the initial sample of uranium was 160 g.
Answer:
c) those caused by parasites
Answer:
The height of the water slide is 0.878 m
Explanation:
Given that,
Distance = 2.52 m
Suppose Children slide down a friction less water slide that ends at a height of 1.80 m above the pool.
We need to calculate the time
Using equation of motion

Put the value in the equation




We need to calculate the velocity
Using formula of velocity

Put the value into the formula


We need to calculate height
Using conservation of energy


Put the value into the formula


Hence, The height of the water slide is 0.878 m.