Question

A glob of slime is launched or dropped from the edge of a cliff. Which of the graphs in figure 7-22 could possibly show how the kinetic energy of the glob changes during its flight?

Short answer

For launch, it is represented by graph (e).

For drop, it is represented by graph (f).

Step-by-step solution

The given data

A glob of slime is launched or dropped from the edge of a cliff.

Understanding the concept of the kinetic energy

We have to use the formula of kinetic energy to decide which graph is suitable. Using this concept of speed, we can get the required graph for both the cases of launch and drop of the body from the cliff.

Formula:

The kinetic energy of the body, $\mathrm{KE}=\frac{1}{2}{\mathrm{mv}}^2$ (i)

Calculation of the kinetic energy graphs for the given cases of launch and drop

When an object is launched with some initial velocity, it has some initial kinetic energy. Then velocity goes on decreasing because of acceleration due to gravity, and that is why kinetic energy also decreases using equation (i).

From above diagrams, we can see that only graph (e) shows the type of nature when the object is dropped.

Initially, the object is at rest, so kinetic energy is also zero. Then the velocity increases because the acceleration due to gravity and velocity is in the same direction. As velocity increases, kinetic energy also increases using equation (i).

Thus, graph (f) shows this type of nature for the object being dropped.

We can see the parabolic shape of the graph. It is because kinetic energy is dependent on the square of the velocity.