Chapter 11, Problem 73A

(a)

To determine

To draw:The energy bar diagram of the system.

To identify: Whether the mechanical energy will change or not. If yes, then state the amount of energy changed.

Answer to Problem 73A

The energy bar diagram of the system is shown in Figure 1.

Yes, the mechanical energy will change.

The change in mechanical energy is $3,175\text{ J}$ .

Explanation of Solution

Given:

The force applied due to the person is $F=635\text{ N}$ .

The height of the ladder from the reference level is $d=5.0\text{ m}$ .

Formula used:

The expression for the potential energy is,

  $PE=Fd$

Here, $F$ is the force and $d$ is the distance.

Calculation:

Consider ground as the reference level. At the reference level the person has no potential and kinetic energy.

When the person starts to climb the ladder and stops at the top, the person contains the gravitational potential energy.

The energy bar diagram for the given specification is shown below.

  

Figure 1

Initially the person has no mechanical energy. After the person climbs the top, there will be a gravitational potential energy.

Hence, the mechanical energy will be changed.

The change in mechanical energy will be,

  $\begin{array}{l}PE=Fd\\ PE=\left(635\text{ N}\right)\times \left(5.0\text{ m}\right)\\ PE=3,175\text{J}\end{array}$

(b)

To determine

The source of the mechanical energy.

Answer to Problem 73A

The source of the mechanical energy is the person.

Explanation of Solution

Given:

The force applied due to the person is $F=635\text{ N}$ .

The height of the ladder from the reference level is $d=5.0\text{ m}$ .

Formula used:

The expression for the potential energy is,

  $PE=Fd$

Here, $F$ is the force and $d$ is the distance.

Calculation:

Refer to part (a).

The change in mechanical energy is $3,175\text{ J}$ .

Initially there is no kinetic energy or potential energy. After the person climbs the top, there will be a gravitational potential energy. So the energy is from the internal energy of the person.

Conclusion:

Thus, the source of the mechanical energy is the person.