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

Asap and show ! a 14 kg rock starting from rest free falls through a distance of 5.0 m with no air resistance. find the momentum change of the rock caused by its fall and the resulting change in the magnitude of earths velocity. earth mass is 6.0 * 10^24 kg. show your work assuming the rock earth system is closed.

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Una carga puntual de 3 x 10-6 c se coloca a 12 cm de una segunda carga puntual de - 1,5 x 10-6 c. calcular la magnitud fuerza eléctrica entre las cargas