An object is moving initially with a velocity of 4.7 m/s . after 3.9 s the object's velocity is -2.1 m/s . what is the object's average acceleration during this time?
i believe that the vf is -2.1 m/s vi should be 4.7 m/s and the t should be 3.9s but its #confused

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.

What sort of waves exhibit the doppler effect?

Two point charges are separated by a certain distance. how does the strength of the electric field produced by the first charge, at the position of the second charge, change if the second charge is doubled? a. the field does not change b. the field strength decreases by half. c. the field strength doubles d. the field strength quadruples