I don't understand, how do you do this question

Anton created a chart listing different types of materials.which best complete the chart? (a)x: copper y: glass(b)x: rubber y: copper(c)x: paper y: silicon(d)x: silicon y: glass

Asmall 12.00g plastic ball is suspended by a string in a uniform, horizontal electric field with a magnitude of 10^3 n/c. if the ball is in equilibrium when the string makes a 30 ° angle with the vertical, what is the net charge on the ball?

A51 kg woman skis down a hill and her kinetic energy is 9.96e4 j. what is her speed?