You can see your image in front of mirror but not in the wall .why?

The least penetrating form of radiation is

Ihave a density of 1.61g/cm^3 and a mass of 28g. find the missing value

Point charges q1 = 51 µc and q2 = −27 µc are placed 1.0 m apart, with q2 on the right. what is the force (in n) on a third charge q3 = 19 µc placed midway between q1 and q2? (assume the positive direction is to the right. indicate the direction with the sign of your answer.)