Why are scientific theories changed but never thrown away

1. jay fills a wagon with sand (about 20 kg) and pulls it with a rope 30 m along the beach. he holds the rope 25° above the horizontal. the rope exerts a 20-n tension force on the wagon. how much work does the rope do on the wagon?

Discuss how the hardness or softness of the landing surface is related to the time required to stop the egg

Acoil suspended freely, points in some direction when no current is passed through it . can you tell what will happen when a current is passed though it?