1. A 2.0 kg mass is lifted 4.0 m above the ground. Find the change in gravitational energy. 2. Hulky and Bulky challenge each other to a race up a flight of stairs (Ah = 4.0 m). Hulky, whose mass is 120 kg, makes the climb in 3.0 s; while Bulky, 150 kg, took 4.0 s to make the climb. Who is more powerful? 3. A car accelerates from 30 mi/hr to 60 mi/hr. How many times greater is the car's kinetic energy at the higher speed compared to the kinetic energy at the slower speed?