Alarge truck and a compct car are both driving down the
samehill at the same constant speed. the truck's brakes are more
likelyto smoke(to overheat). why?

Explanation:

The friction force acting on the body depends on the mass of the body, here the mas of truck is very large as compared  to the car, so the friction force acting on the truck is large then the car. So, the amount of heat generated by the truck is more than the car and the truck overheated more.

adding a(n) to an electric circuit would increase the magnetic field around a wire;

b. solenoid

a solenoid is a type of electromagnet whose purpose is to generate a controlled magnetic field.

if the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.

a.   mass number from atomic number