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. 157 bar/2270 psi
Explanation:
Calculation to determine what we should head back when either of our SPGs read
SPGs=200 bar -[200 bar-(50 bar + 20 bar)]÷1/3]
SPGs=200 bar-[(200 bar-70 bar)÷1/3]
SPGs=200 bar-(130 bar÷1/3)
SPGs=200 bar-43 bar
SPGs=157 bar/2270 psi
Therefore based on the above calculation we should head back when either of our SPGs read 157 bar/2270 psi
Impulse = change in momentum
The answer is 0.
Answer: If one bulb goes out the other bulbs stay lit.
If there is a break in one branch of the circuit, current can still flow through the other branches.
Explanation:
The correct option is C. i.e. <span>Using more coils of wire
</span>
Explanation:
The strength of an electromagnet can be increased in the following ways:
1. By increasing the number of coils.
2. By increasing the current/voltage
3. Using an iron core, increases the strength of the electromagnet.