To find out how much time the person takes to cover the entire length of the escalator, we need to combine the speeds of the escalator and the person.

Given:

• Speed of the escalator: $11 \, \text{ft/sec}$
• Speed of the person walking on the escalator: $3 \, \text{ft/sec}$
• Length of the escalator: $140 \, \text{ft}$

Since the person is walking in the same direction as the escalator is moving, we add the two speeds:

$\text{Total speed} = 11 \, \text{ft/sec} + 3 \, \text{ft/sec} = 14 \, \text{ft/sec}$

Now, to find the time taken to cover the length of the escalator, we use the formula:

$\text{Time} = \frac{\text{Distance}}{\text{Speed}}$

$\text{Time} = \frac{140 \, \text{ft}}{14 \, \text{ft/sec}} = 10 \, \text{seconds}$

Answer:

The person takes 10 seconds to cover the entire length of the escalator.

Would you like further details or clarifications?

Here are 5 related questions to explore:

1. What if the escalator was moving slower, at 5 ft/sec? How would the time change?
2. If the person walks in the opposite direction of the escalator, how would you calculate the time taken?
3. How long would it take if the person stood still on the escalator?
4. What would happen if the person walks at 6 ft/sec instead of 3 ft/sec?
5. How far will the person walk in 5 seconds if the escalator is turned off?

Tip: When solving motion problems involving multiple moving elements, always consider their relative speeds.