If two uncharged objects are rubbed together and one of them acquires a negative charge, then the other one
a. remains uncharged
b. acquires a positive charge equal to twice the negative charge
c. also acquires a negative charge
d. acquires a positive charge acquires a positive charge equal to half the negative charge

Idon’t quite understand this problem

Suppose a force of 60 n is required to stretch and hold a spring 0.1 m from its equilibrium position. a. assuming the spring obeys hooke's law, find the spring constant k. b. how much work is required to compress the spring 0.5 m from its equilibrium position? c. how much work is required to stretch the spring 0.6 m from its equilibrium position? d. how much additional work is required to stretch the spring 0.1 m if it has already been stretched 0.1 m from its equilibrium? a. kequals 600

What practical value did astronomy offer to ancient civilizations?