Question

A large box is taken to a height of $8m$, when energy spent is $64,000J$. The mass of the box is:

• A. $400kg$
• B. $800kg$
• C. $700kg$
• D. $1600kg$

Answer 1

The correct option is B

$800kg$

Step 1: Given data

height,$h=8m$

Mass of box, $m=?$( To be calculated)

Acceleration due to gravity, $g=10m{s}^{-2}$

Energy spent, $P.E.=64,000J$

Step 2: Formula for potential energy

$$\begin{gathered} PotentialEnergy=mass\times accelerationduetogravity\times height \\ \therefore P.E.=m\times g\times h \end{gathered}$$

Step 3: By putting the values in the above expression, we get

$$\begin{gathered} P.E.=m\times g\times h \\ \Rightarrow 64,000J=m\times 10m{s}^{-2}\times 8m \\ \Rightarrow m=\frac{64,000J}{8m\times 10m{s}^{-2}} \\ \Rightarrow m=800kg \end{gathered}$$

Therefore, the mass of the box is $800kg$.

Hence, the correct answer is option (B).