Before rock climbing, Donald, who is 5.5 ft. tall, wants to know how high he will climb. He places a mirror on the ground and walks 11 feet backwards until he can see the top of the cliff in the mirror. If the mirror is 42 feet from the cliff side, determine the height of the cliff

Amass weighing 16 pounds stretches a spring 8/3 feet. the mass is initially released from rest from a point 2 feet below the equilibrium position, and the subsequent motion takes place in a medium that offers a damping force that is numerically equal to 1/2 the instantaneous velocity. find the equation of motion if the mass is driven by an external force equal to f(t)=cos(2t).