Can someone help me with question 7a and 7b? it would mean alot.

Which statement best explains why an object weight less on mercury than it does on earth

Aplane flying horizontally at an altitude of 1 mile and a speed of of 500mih passes directly over a radar station. find the rate at which the distance from the plane to the station is increasing when it is 2mi away from the station.

What is a subatomic particle with a negative charge and very little mass?