Question 260: Laws of Motion

Question

A disc of mass 10 g is kept floating horizontally by throwing 10 marbles per second against it from below. If the mass of each marble is 5 g . What will be velocity with which the marble are striking the disc? Assume that, the marble strikes the disc normally and rebound downwards with the same speed.

Accepted Answer

$F=\frac{\Delta p}{\Delta t}=\frac{\Delta(m n v)}{\Delta t}$
Here, $m=$ mass of one marble $=5 \mathrm{~g}$
$$\begin{aligned}
\frac{n}{\Delta t} & =	ext { number of molecules striking per second } \
& =10 \
	herefore M g & =m\left(\frac{n}{\Delta t}ight)|\Delta v|
\end{aligned}$$
Here, $M=$ mass of disc
$$\begin{aligned}
\left(10 	imes 10^{-3}ight)(9.80) & =\left(5 	imes 10^{-3}ight)(10) 2 v \
	ext { or } \quad v & =0.98 \mathrm{~m} / \mathrm{s}
\end{aligned}$$

Answer

$2.98 \mathrm{~m} / \mathrm{s}$

Answer

$0.98 \mathrm{~m} / \mathrm{s}$

Answer

$0.49 \mathrm{~m} / \mathrm{s}$

Answer

$1.96 \mathrm{~m} / \mathrm{s}$

Laws of Motion

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