A force F = 3i + 7j + 7k acts on a 2 kg mobile object that moves from an initial position of D1 = 3i – 2j + 5k to a final position D2 = - 5i + 4j + 7k in 4 seconds. What is the average power due to the force during that 4 s interval? -

How fast would a 30-kg kid need to run in order to have the same kinetic energy as an 8.0-g bullet fired at 400 m/s, in m/s? Your answer needs to have 2 significant figures, including the negative sign in your answer if needed. Do not include the positive sign if the answer is positive. No unit is needed in your answer, it is already given in the question statement.

1. A 4.0 kg particle is moving at a velocity v = V2î – V2ĵ + 3k m/s. (a) (b) What is the particle's kinetic energy at this moment? What is the net work done on the particle if its velocity changes to - V2î + 3k m/s? V = - Assume that a force in the x y plane acts on the particle to slow it down (imagine (c) that this force is a type of friction). Will the particle's kinetic energy become zero under the influence of this force? Explain your answer.

A railroad locomotive accelerates a 95,000-kg railcar from 10 m/s to 25 m/s in 90 seconds. What was the average power transferred to the boxcar during this process? 25 MW 280 kW 330 kW 2.3 MW 48 kW