the half-life of strontium is 28 years. How long will it take so the number of nuclei of this isotope will decrease 8 times.

What is the weight of a feather (mass = 0.0001 kg) that floats through earth's and the moon's atmospheres?

A0.750 kg aluminum pan is removed from the stove and plunged into a sink filled with 10.0 kg of water at 293 k. the water temperature quickly rises to 297 k. what was the initial temperature of the aluminum pan? the specific heat of aluminum is ca = 900 j/(kgk) and water is cw = 4190 j/(kgk)

Exercise 2. find the wavelength of a photon emitted when an electron jumps from the n = 3 energy level down to the n = 2 energy level. where is this photon in the electromagnetic spectrum?