Question

A $0.4\, kg$ mass takes $8 \,s$ to reach ground when dropped from a certain height ' $P$ ' above surface of earth. The loss of potential energy in the last second of fall is ___$J$.
$\left(\right.$ Take $\left.g =10 \,m / s ^2\right)$

Answer 1

Displacement is $8^{\text {th }}$ sec.
$ S _8=0+\frac{1}{2} \times 10 \times(2 \times 8-1)$
$ S _8=5 \times 15$
$ \Delta U =0.4 \times 10 \times 5 \times 15$
$ \Delta U =20 \times 15=300$