Question

1. calculate the power generated after $t = 120$ s.

work vs. time

1. identify if the work done on the block is zero, negative or positive.

a. a person lowering a block at constant low speed and putting it on the floor.
b. a heavy block is pushed with a force that does not move the block at all.
c. a person carries a block and walks in a straight line.
d. a block is held stationary 5 m above the ground by a string.

Explanation:

Problem 4

Step1: Recall power formula

Power is defined as $P = \frac{W}{t}$, where $W$ is work done, $t$ is time.

Step2: Read values from graph

At $t=120\ \text{s}$, $W=100\ \text{J}$.

Step3: Calculate power

Substitute values into the formula:
$P = \frac{100}{120}$

a. The force applied by the person acts opposite to the block's downward displacement, so work is negative.
b. No displacement occurs despite applied force, so work is zero.
c. The upward force on the block is perpendicular to the horizontal displacement, so work is zero.
d. No displacement occurs while holding the block, so work is zero.

Answer:

$\frac{5}{6}\ \text{W} \approx 0.83\ \text{W}$

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Problem 5