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4-1.Newton's Laws of Motion
hard
Figure shows a boy on a horizontal platform $A$ on a smooth horizontal surface, holding a rope attached to a box $B$ . Boy pulls the rope with a constant force of $50\ N$ . (boy does not slip over the platform). The combined mass of platform $A$ and boy is $250\ kg$ and that of box $B$ is $500\ kg$ . The velocity of $A$ relative to the box $B$ , $5\ s$ after the boy on $A$ begins to pull the rope, will be ............ $m/s$
A
$1$
B
$1.5$
C
$2$
D
$0.5$
Solution
$a_{1}=\frac{1}{5} \mathrm{m} / \mathrm{s}^{2} \mathrm{a}_{2}=\frac{1}{10} \mathrm{m} / \mathrm{s}^{2}$
$\mathrm{v}_{1}=5 \times \frac{1}{5}=1 \mathrm{m} / \mathrm{s} \quad \mathrm{v}_{2}=5 \times \frac{1}{10}=\frac{1}{2} \mathrm{m} / \mathrm{s}$
$\mathrm{v}_{12}=1.5 \mathrm{m} / \mathrm{s}$
Standard 11
Physics
