An experimental rocket sled weighs 5200 ib abd is propelled by six rocket motors each with an impulse rating of 8600 ib-sec. The rockets are fired at 1 sec intervals, and the duration of each rocket firing is 2sec. if the velocity of the sled 10 sec from the start is 200mi\hr, determine the time average R of the total aerodynamic and mechanical resistance to motion. neglect the loss of mass due to exhausted fuel compared with the mass of the sled.