A machine used 20 J of energy to make a bicycle start. However, 6 J of energy was
wasted as heat. What is the percentage
efficiency of the machine?
a 30%
b 75%
C 70%
d 60%​

Four objects each with charge +2.0×10−7c are located at the corners of a square whose sides are 2.0 m long. part a what quantities can be determined using this information? check all that apply. the electric force on a charged object placed at the center of the square. the mass of each object. the total electric potential energy of the system consisting of the four charged objects. part b find the electric force on a charged object placed at the center of the square.