The speed of an electron in an orbit around hydrogen atom is 2.2*10^6 ms^-1.It takes 1.5*10^-16 s for the electron to complete one orbit. Calculate the radius of the orbit. please help me ASAP!!

Write the fraction 9/50 as a decimal if needed round to the nearest hundredth

How many kilometers are equal to 5 miles? use 1 mile ≈ 1.61 kilometers. !

The position of a moving particle is given by the position function: f(t)=-9t-t^2-0.2t^3+0.1t^4 a. at what time does the particle reverse direction? b. when is the displacement positive? (round one decimal place and answer in interval notation) c. when is the displacement negative? (round one decimal place and answer in interval notation) d. when is the particle’s acceleration positive? (round one decimal place and answer in interval notation) e. when is the particle’s acceleration negative? (round one decimal place and answer in interval notation)