An electroscope is a device that has small gold foil strips suspended from a metal rod. a student brings a negatively charged rod near the top of a neutral electroscope. the student then briefly touches a hand to the top of the electroscope before removing the charged rod. the foil strips of the electroscope now spread apart. the student then brings a different rod near the top of the electroscope. the leaves of the electroscope move closer together (see below). the new rod must have a net charge that is

1) positive.
2) negative.
3) neutral.
4) not enough information.

Awater balloon launcher uses an elastic band with a spring constant of 115 n/m to use thee launcher you stretch thee band back with a balloon n it the water balloons have a mass of 1.3 kg a) if you stretch the band by 0.8 m, what elastic force will the band exert? b) with the band stretched 0.8 m, how much elastic potential energy is stored in the spring? c) if you release the band, it pushes forward. what is the kinetic energy of the balloon when it reaches the natural length of the band? d) what is the speed of the balloon when it reaches the natural length of the band?