A model rocket is fired vertically upward from rest. Its acceleration for the first three seconds is a(t) = 66 t, at which time the fuel is exhausted and it becomes a freely "falling" body. 15 seconds later, the rocket's parachute opens, and the (downward) velocity slows linearly to -23 ft/s in 5 s. The rocket then "floats" to the ground at that rate.
Determine the position function s and the velocity function v (for all times t).

Electric field of the earth. the earth has a net electric charge that causes a field at points near its surface equal to 150 n> c and directed in toward the center of the earth. (a) what magnitude and sign of charge would a 60-kg human have to acquire to overcome his or her weight by the force exerted by the earth’s electric field? (b) what would be the force of repulsion between two people each with the charge calculated in part (a) and separated by a distance of 100 m? is use of the earth’s electric field a feasible means of flight? why or why not?

What is the weight of a 8-kg substance in n, kn, kg·m/s2, kgf, lbm·ft/s2, and lbf?

Where do magnetic lines of force enter earth?