A student charges a balloon and then brings it near a metal sphere hanging from the ceiling. She brings it near the sphere, but does not touch. The sphere moves toward
the balloon. What are the charges on the balloon and the metal sphere?
a) The balloon has a positive charge and the metal sphere has a negative charge.
b) The balloon has a negative charge and the metal sphere has a positive charge.
c) Both are negatively charged.
d) Both are positively charged.

Two polarizers are oriented at 40∘ to each other and plane-polarized light is incident on them. if only 16 percent of the light gets through both of them, what was the initial polarization direction of the incident light?

Sobre transformações cíclicas, são feitas algumas afirmações, determine quais estão corretas. i – a variação de energia interna em uma transformação cíclica é nula; ii – o trabalho, em uma transformação cíclica, é sempre positivo; iii – ao completar um ciclo, o gás tem a mesma temperatura com a qual começou a transformação; iv – uma transformação cíclica é, obrigatoriamente, composta de transformações conhecidas, como adiabática, isocórica, etc: a) i e iii b) i e ii c) ii e iii d) i e iv e) iii e iv

Consider a system with two masses that are moving away from each other. why will the kinetic energy differ if the frame of reference is a stationary observer or one of the masses?