1) An elevator with a person in it is being pulled upwards by a cable. Identify all interaction forces in the system. Consider your system to consist othe cable, elevator, the Earth and the person. The Earth pulls down on the elevator with force Mg and the elevator pulls up the Earth with force Mg. Find the other four pairs of forces. I got the person pushing down on the elevator and the elevator pushing up with a Normal force. The cable pulls the elevator up with a tension force and the elevator pulls the cable down with the same force. The earth pulls the person down with mg and the person pulls the earth up. Are the 3 I have correct? What is the 4th one? 2) A block is initially held stationary on a ramp by friction. Suddenly a force F is applied and is gradually increased from 0 up until the block is accelerating up the incline. During the entire time period, describe the changes in the magnitude and direction of the frictional force extered by the incline on the block. I know that if the block's mass stays the same, and it acceleration increase going up, F will increase in magnitude. On the contrary, this acceleration will be against gravity, reducing the downward net force. Since friction |f_k| = (mu_k) *|n|, friction will decrease since n decrease with gravity. Is my reasoning correct? How do I know the magnitude and direction changes though?