Work and Energy
2-7
2. The trick to doing this problem is to remember that you need to talk about the Total energy being conserved for the entire system.
3. The initial mechanical energy here is just the kinetic energy of the Sled.
The final mechanical energy of the sled is zero, because of friction. The change in the mechanical energy of the snow-sled system is thus,
The only work that does work is the kinetic friction. The normal force exerted by the snow on the sled equals the weight of the sled,
The magnitude of the frictional force is then,
Now apply this force to work equation and solve for x
4. In this problem, we have two forces. Fapp and friction. The total work done is these two forces added together. Once we have the total work done, we can use that to find the velocity by setting the total work done equal to the change in kinetic energy.
5. Here just calculate the velocity, then from there calculate the power.
6. Here just use the fact that the change in potential equals the amount of work done.
7. This problem is a little tricky, but once you see it, you should understand. For the first part, you want to find the frictional force. The way to do this is to see that the only force doing work on the bullet is friction, therefore, we can calculate the work done by friction and set it equal to change in kinetic energy.
For the second part, just use the fact that average velocity equal the distance divided by the time.
