a crane lifts a 3,000 kg beam of concrete from the ground to a height of 50 m. what work is being done on the concrete?

The following statements are about the electroscope. select all that are true. if an electroscope were given a positive charge beforehand, the leaves would move closer together if a positively charged object were brought near. when a properly prepared electroscope is used to determine the type of charge on an object, the total charge on the electroscope changes when the charged object is brought near (but not touching) the electroscope. depending on how the electroscope is prepared beforehand, the leaves can either move together or move apart when negative charge is brought near. an electroscope must first be given a known type of charge before it can be used to identify the types of charges on objects brought near it. when properly prepared, the leaves on an electroscope will always move further apart when negative charge is brought near. the leaves of an electroscope will move apart if it is given either a positive or a negative charge.