Work Power and Energy 5 Question 11
14. Consider an elliptically shaped rail $P Q$ in the vertical plane with $O P=3$ $m$ and $O Q=4 m$. A block of mass $1 kg$ is pulled along the rail from $P$ to $Q$ with a force of $18 N$, which is always parallel to line $P Q$ (see figure). Assuming no frictional losses, the kinetic energy of the block when it reaches $Q$ is $(n \times 10) J$. The value of $n$ is (take acceleration due to gravity $=10 ms^{-2}$ )
(2014 Adv.)
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Answer:
Correct Answer: 14. $50 J$
Solution:
- From work-energy theorem
Work done by all forces = change in kinetic energy
$$ \text { or } \quad W _F+W _{m g}=K _f-K _i $$
$$ \begin{aligned} & 18 \times 5+(1 \times 10)(-4)=K _f \\ & 90-40=K _f \text { or } K _f=50 J=5 \times 10 J \end{aligned} $$
