Question

A 4.5 kg object is lifted from the floor and placed on a shelf that is 0.9 m above the floor. What was the work done in lifting the object?
Group of answer choices

49 J

1.2 J

40 J

0.5 J

Answer 1

To find the work done in lifting the object, we can use the formula for gravitational potential energy, which is given by:

\[
W = m \cdot g \cdot h
\]

where:
- \( W \) is the work done,
- \( m \) is the mass of the object (in kg),
- \( g \) is the acceleration due to gravity (approximately \( 9.81 \, \text{m/s}^2 \)),
- \( h \) is the height (in m) the object is lifted.

For this problem:
- \( m = 4.5 \, \text{kg} \)
- \( g = 9.81 \, \text{m/s}^2 \)
- \( h = 0.9 \, \text{m} \)

Now we can plug these values into the formula:

\[
W = 4.5 \, \text{kg} \cdot 9.81 \, \text{m/s}^2 \cdot 0.9 \, \text{m}
\]

Calculating this:

\[
W = 4.5 \cdot 9.81 \cdot 0.9
\]

\[
W \approx 39.63 \, \text{J}
\]

Rounding to two significant figures, we find:

\[
W \approx 40 \, \text{J}
\]

So the work done in lifting the object is approximately **40 J**.

The correct answer from the options provided is:

**40 J**