A simple radioactive element with half life of two minutes initially contains 60×10^6atoms. calculate the time it would take for the atom to reduced to 7.5×10^6atoms

t=360S

Explanation:

T½=2mins

No=60x10^6

t=?

Nr=7.5x10^6

Nr/No=1/2^n

7.5x10^6/60x10^6=(1/2)^n

0.125=2^- n

Take log to bothsides

Log10^0.125=log10^2^- n

Ln0.125= -nln2

- 2.079= - 0.693n

N=2.079/0.693

N=3

N=t/T

t=nxT

t=3x2x60

t=360s

r=rho l/a where a is the area, l is the length and rho is resistivity so the greater the area the lesser the resistance thats why the earth pin is thicker bcos current follow the shortest path, so less resistive .

b. lifting dumbbell weight at 20-degree angle from the body after a 45-degree angle