Aball is thrown onto a rough floor at an angle theta. if it rebounds at an angle phi and the coefficient of kinetic friction is determine: (a) the coefficient of restitution e. (b) further simplify the expression if theta = phi = 45°. (c) from the previous part, determine the coefficient of friction if = 0.6. neglect the size of the ball. hint: show that during impact, the average impulses in the x and y directions are related by = . since the time of impact is the same, δ = δ or = .

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?