Question 8.10: Interpreting the Energy Bars The energy bar charts in Figure......
Interpreting the Energy Bars
The energy bar charts in Figure 8.13 show three instants in the motion of the system in Figure 8.12 and described in Example 8.9. For each bar chart, identify the configuration of the system that corresponds to the chart.
In Figure 8.13 \mathrm{a}, there is no kinetic energy in the system. Therefore, nothing in the system is moving. The bar chart shows that the system contains only gravitational potential energy and no internal energy yet, which corresponds to the configuration with the darker blocks in Figure 8.12 and represents the instant just after the system is released.
In Figure 8.13 \mathrm{~b}, the system contains four types of energy. The height of the gravitational potential energy bar is at 50 \%, which tells us that the hanging block has moved halfway between its position corresponding to Figure 8.13a and the position defined as y=0. Therefore, in this configuration, the hanging block is between the dark and light images of the hanging block in Figure 8.12. The system has gained kinetic energy because the blocks are moving, elastic potential energy because the spring is stretching, and internal energy because of friction between the block of mass m_{1} and the surface.
In Figure 8.13 \mathrm{c}, the height of the gravitational potential energy bar is zero, telling us that the hanging block is at y=0. In addition, the height of the kinetic energy bar is zero, indicating that the blocks have stopped moving momentarily. Therefore, the configuration of the system is that shown by the light images of the blocks in Figure 8.12. The height of the elastic potential energy bar is high because the spring is stretched its maximum amount. The height of the internal energy bar is higher than in Figure 8.13 b because the block of mass m_{1} has continued to slide over the surface.