Question

A mason worker throws the bricks to a height of 10m, at which the bricks reach with a velocity of ${6ms}^{-1}$. The percentage of energy he is nearly ${(g=10ms}^{-2})$

• A. 15%
• B. 18%
• C. 220%
• D. 36%

Answer 1

Answer: (A)

15%

Increase in $potential$ energy is $PE=mgh=m\times 10\times 10=100m$

and the Kinetic energy at that point (top point) is $KE=\frac{m{v}^2}{2}=\frac{m\times 36}{2}=18m$

so total work done by the man will be $W=PE+KE=118m$

So the percentage of $waste$(due to this KE because the brick don't need to go further so the velocity will be go in vein)

in energy will be $\frac{KE}{W}\times 100$ % =$15.25$ %