# Solve the following :

Question:

A man of mass $50 \mathrm{Kg}$ starts moving on the earth and acquires a speed of $1.8 \mathrm{~m} / \mathrm{s}$. With what speed does the earth recoil? Mass of earth $=6 \times 10^{24} \mathrm{Kg}$.

Solution:

Conservation of lin. Momentum (C.O.L.M)

$0=M_{E} V_{E}+M_{M} V_{M}$

M-Man

E-Earth

$V_{E}=\frac{-M_{M} V_{M}}{M_{E}}=\frac{-50 \times 1.4 \times 10^{7}}{6 \times 10^{24}}$

$=-15 \times 10^{-24} \mathrm{~m} / \mathrm{s}$