What makes up an electromagnetic wave? a. compressions moving through space b. changing electric and magnetic fields c. a changing electric field only d. a changing magnetic field only

Why do astronauts in the space shuttle weigh less?

In which of the following is positive work done by a person on a suitcase

Aresistor with an unknown resistance is connected in parallel to a 9 ω resistor. when both resistors are connected in parallel to an emf source of 21 v, the current through the unknown resistor is measured with an ammeter to be 4 a. what is the resistance of the unknown resistor? answer in units of ω.