Wasted Energy




1) Imagine a squirrel falling from a branch, reaching terminal velocity on the way down, and being stopped by the ground. Describe which forces are doing work, whether the work is positive or negative, and the relative magnitudes of the forces in each of these three stages.



2) Fire a projectile off a cliff 15 m in height. The projectile is launched at some angle above the horizontal. If the initial speed of the projectile is 55 m/s, what is its speed when it lands?



3) Drop an object a distance of 1.5 m, with the object starting at rest. Using energy conservation (not the kinematic equations) find its speed when it lands. Assume 75% efficiency.



4) A child is playing on a swing. At the lowest point, the speed of the swing is 3.0 m/s. How high above this low point will the child rise? Assume 65% efficiency.



5) How much energy is needed to speed a 1200 kg car from 0 to 25 m/s in 7.5 seconds? Assume 25% efficiency and level ground.



6) A basketball player shoots a 0.600 kg ball from a height 2.00 m above the floor at a speed of 7.20 m/s. The ball passes through the net 3.00 m above the floor at a speed of 4.20 m/s. What is the work done on the ball by air resistance?



7) A group of people is taking a white-water rafting trip down a river. The mass of the raft and everyone aboard is 945 kg. The raft enters the rapids with a speed of 2.25 m/s and drops through a vertical distance of 20.0 m before leaving the rapids. Water resistance does -1.60 105 J of work. What is the speed of the raft when it exits the rapids?