1. An object whose mass is 400 kg is located at an elevation of 25 m above the surface of the earth. For g 5 9.78 m/s2, determine the gravitational potential energy of the object, in kJ, relative to the surface of the earth.

2. An object whose weight is 100 lbf experiences a decrease in kinetic energy of 500 ft ? lbf and an increase in potential energy of 1500 ft ? lbf. The initial velocity and elevation of the object, each relative  to  the  surface  of  the  earth,  are 40 ft/s and 30 ft, respectively. If g 5 32.2 ft/s2, determine

(a) the final velocity, in ft/s.

(b) the final elevation, in ft.

3. A 2.5 3 3.5 3 6 in. brick whose density is 120 lb/ft3 slips off the top of a building under construction and falls 69 ft. For g 5 32.0 ft/s2, determine the change in gravitational potential energy of the brick, in ft ? lbf.