6. A boulder rests on a ledge 31.2 m above a lake. If it has 2.65 × 105 J of gravitational potential energy relative to the lake surface, what is the mass of the boulder? Show all your work.7. On a highway, a car with a mass of 1.1 × 103 kg is travelling at 25 m/s. What is the kinetic energy of the car? Show all your work. 8. A girl is travelling on her bike at a speed 2.54 m/s. If the girl and her bike have a kinetic energy of 193 J, what is the combined mass of the girl and her bike? Show all your work. 9. A hockey puck has a mass of 0.20 kg. If the hockey puckis moving with 75 J of kinetic energy, what is its speed? Show all your work.10. a. A 0.430 kg baseball comes off a bat and goes straight up in the air. At a height of 10.0 m, the baseball has a speed of 25.3 m/s. Determine the mechanical energy at this height. Show all your work. b. What is the baseball’s mechanical energy when it is at a height of 8.0 m? Explain. 211. A golfer hits a 42 g ball, which comes down on a tree root and bounces straight up with an initial speed of 15.6 m/s. Determine the height the ball will rise after the bounce. Show all your work. 12. A girl pushes herself up a steep ramp in her wheelchair. She gains a vertical distance of 25.8 m when she reaches the top of the ramp. She turns around and coasts back down the ramp. If the combined mass of the girl and her wheelchair is 64.6 kg, what would be her coasting speed at the bottom of the ramp? Show all your work.