Trường hợp nào dưới dây có thể coi là chất điểm A. trái đất trong CĐ tự quay quanh mình nó với nhau
B. hai hòn bi lúc va chạm
C. người nhảy cầu lúc đang rơi xuống nước
D. giọt nước mưa lúc đang rơi

Mutt and jeff are running along a path each pushing a cart loaded with rocks. if mutt's wagon has a mass two times greater than jeff's and they want to stay together, arriving at their destination at the same time, what must happen? a) jeff should slow down so mutt can catch up. b) mutt must use half as much force to push his cart. c) mutt must use twice as much force to push his cart. d) mutt and jeff will use the same force, but mutt will take bigger steps.