Why do all objects hit with the same velocity (ignoring air resistance) if dropped from the same height?

Simple machines can a. increase force only b. decrease force only c. increase or decrease force

What are atoms of the same element with varying number of neutrons

The atoms in a nickel crystal vibrate as harmonic oscillators with an angular frequency of 2.3 × 1013 rad/s. the mass of a nickel atom is 9.75 × 10-26 kg. what is the difference in energy between adjacent vibrational energy levels of nickel? (h = 6.626 × 10-34 j • s, , 1 ev = 1.60 × 10-19 j)