Gravitational Potential Energy

From the question: mass $m=4$ kg, height $h=0.75$ m, and gravitational field strength $g=10$ N/kg.

The formula for gravitational potential energy is $GPE=mgh$. Substituting: $GPE=4\times 10\times 0.75$

$GPE=4\times 10\times 0.75=30\text{ J}$

The cat's gravitational potential energy is 30 J. Always remember to include the unit (joules).

We need to calculate GPE using $GPE=mgh$ with $m=4$ kg, $g=10$ N/kg, $h=0.75$ m.

300 J would result from $4\times 10\times 7.5$ — this uses $h=7.5$ m instead of $h=0.75$ m, a decimal place error.

40 J would come from $4\times 10\times 1$ — this incorrectly rounds $h=0.75$ m up to 1 m, giving the wrong answer.

3 J would result from only multiplying $4\times 0.75=3$, forgetting to include $g=10$ N/kg in the calculation.

30 J is correct: $GPE=4\times 10\times 0.75=30$ J.

GPE is calculated using $GPE=mgh$, where $h$ is the height above a chosen reference level. The reference level (where $h=0$) can be chosen differently for different problems.

Since $h$ is measured from a chosen zero point — such as the floor, a table, or sea level — changing the reference level changes the value of $h$ and therefore the value of GPE. This means GPE has no single absolute value.

The correct statement is that GPE depends on the chosen reference level for zero height. What matters in physics problems is typically the change in GPE, which remains the same regardless of the chosen reference.

The question asks why GPE does not have a single absolute value — this relates to how height $h$ is defined in the formula $GPE=mgh$.

'GPE cannot be measured accurately' is incorrect. GPE can be calculated very precisely using $GPE=mgh$; the issue is not about instrument accuracy.

'GPE only exists when moving' is wrong. GPE is potential energy — it is stored in a stationary object due to its position, not its motion.

'GPE changes every second due to Earth's rotation' is not a concept from physics at this level. Earth's rotation does not cause GPE to fluctuate second by second in standard problems.

'GPE depends on the chosen reference level for zero height' is correct. Since we choose where $h=0$, the absolute value of GPE is arbitrary — only changes in GPE are physically meaningful.