How much work is done against the gravitational force on a 3.0 kg object when it is carried from the ground…

Analysis

To solve this problem, we need to calculate the work done against gravity. In physics, when an object is lifted vertically, the work done is equal to the change in its gravitational potential energy.

Concept

The formula for work done ($W$) against gravity is:

Where:

• $m$ = mass of the object (in kg)
• $g$ = acceleration due to gravity (standard value is $10 \, \text{m/s}^2$ for JAMB calculations, unless specified as $9.8 \, \text{m/s}^2$)
• $h$ = vertical height (in meters)

Solution

Step 1: Identify the given values.

• Mass ($m$) = $3.0 \, \text{kg}$
• Height ($h$) = $240 \, \text{m}$
• Gravity ($g$) = $10 \, \text{m/s}^2$

Step 2: Apply the formula.

Step 3: Calculate the result.

Step 4: Convert to kilojoules (kJ). Since $1,000 \, \text{J} = 1 \, \text{kJ}$:

Conclusion

Comparing our result to the given options, the correct value is $7.2 \, \text{kJ}$.

Exam Tip

In JAMB Physics, always check if the question implies the use of $g = 10 \, \text{m/s}^2$ or $g = 9.8 \, \text{m/s}^2$. If the options are round numbers, $10 \, \text{m/s}^2$ is almost always the intended value, as it makes calculations much faster and easier to perform without a calculator!