1. An athlete prepares for practice by walking 1390 m in 8.6 min and sprinting 540 m in 4.9 min. Determine the athlete's average speed in metres per second.

2. A 90.0 g object is moved from a shelf 0.7 m high to one that is 3.7 m high. The change in potential energy for the object is __________ .

3. A trophy sits on top of a shelf 1.90 m above the floor. If the trophy has a potential energy of 145 J, its mass is __________ kg.

4. A 400-g soccer ball has a total mechanical energy of 6.50 J. If the soccer ball is travelling at a speed of 4.55 m/s, determine the height of the ball in centimeters.