What is the mechanical energy of a 500 kg rollercoaster car moving with a speed of 3 m/s at the top hill that is 30 my high

An object of dimensions 50 cm x 40 cm x 0.20 cm has a mass 60g. find its density in g/cm3 and kg/ m3

What causes the formation of ocean currents?

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?