What is the difference between a permanent magnet and an electromagnet

(a) assume the equation x = at^3 + bt describes the motion of a particular object, with x having the dimension of length and t having the dimension of time. determine the dimensions of the constants a and b. (use the following as necessary: l and t, where l is the unit of length and t is the unit of time.) (b) determine the dimensions of the derivative dx/dt = 3at^2 + b. (use the following as necessary: l and t, where l is the unit of length and t is the unit of time.)

Glass has a hardness that is in the middle of the hardness scale. what is the hardness of glass?

Your friend increases her force on the desk by 30n . she doesn't change the direction of her push . what happens to the net force on the desk .will the desk accelerate