A hiker of mass 73 kg is going to climb to the top of Mount Tam, which has an elevation of 2,574 ft. a. If the hiker starts climbing at an elevation of 545 ft, what will their change in gravitational potential energy be, in joules, once they reach the top? Assume the zero of gravitational potential energy is at sea level.
b. Repeat the above calculation for the change in gravitational potential energy, but assume the gravitational potential is zero at the top of the mountain.

You have two photos of a person walking. one shows the person at the corner of third and main streets, the other shows the person at the corner of tenth and main streets. there are lampposts at every corner in this town, and the first picture shows it to be 10: 32: 00 exactly. the second picture shows it to be 10: 49: 30. you know three facts: (1) all of the clocks are synchronized; (2) there are exactly 12 equal-sized blocks per kilometer in this town; and (3) the streets that cross main in this area are numbered consecutively, with no interruptions. what is the person’s average speed in kilometers per hour?