PLEASE HELP FAST!! What makes a model not useful? a)if it is in proportion with the object it represents
b)if it is made of a different material than the object it represents
c)if it is not the same mass of the object it represents
d)if it is out of proportion with the object it represents

If you put a helium-filled balloon in the refrigerator, what will happen?

Two 2.0-cm-diameter disks face each other, 1.0 mm apart. they are charged to ±10 nc. what is the electric field strength between the disks? a proton is shot from the negative disk toward the positive disk. what launch speed must the proton have to just barely reach the positive disk?

Ascientist notices that an oil slick floating on water when viewed from above has many different colors reflecting off the surface, making it look rainbow-like (an effect known as iridescence). she aims a spectrometer at a particular spot and measures the wavelength to be 750 nm (in air). the index of refraction of water is 1.3