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5.Work, Energy, Power and Collision
normal
Two ice skaters $A$ and $B$ approach each other at right angles. Skater $A$ has a mass $30\,kg$ and velocity $1\,m/s$ and skater $B$ has a mass $20\,kg$ and velocity $2\,m/s$ . They meet and cling together. Their final velocity of the couple is ............. $\mathrm{m}/ \mathrm{s}$
A
$2$
B
$1.5$
C
$1$
D
$2.5$
Solution
Momentum of skater $\mathrm{A}=30 \times 1=30 \mathrm{kgm} / \mathrm{s}$
Momentum of skater $\mathrm{B}=20 \times 2=40 \mathrm{kgm} / \mathrm{s}$
They are at right angles to each other.
Resultant momentum $=$ $\mathrm{p}$
$(p)^{2}=(30)^{2}+(40)^{2}=900+1600=2500$
or $\mathrm{p}=50 \mathrm{kgm} / \mathrm{s}$
Final velocity $=\frac{p}{\text { Total mass }}$
$=\frac{50}{(30+20)}=\frac{50}{50}=1 \mathrm{m} / \mathrm{s}$
Standard 11
Physics
