How to find the speed of a block which is about to spin about a fixed axis?

Jun 2017
399
6
Lima, Peru
The problem is as follows:

A block which its mass is $5\,kg$ is at rest as indicated. A thin bar of negligible weight has a length of $0.4\,m$ and it links it to point $A$ where there is a mechanism which allows turning about that axis. A force $P=10N$ is applied to the block as depicted. The bar has a moment of $M=3t$. Given these conditions find the speed of the block at $4\,s$.



The alternatives are as follows:

$\begin{array}{ll}
1.&5\,\frac{m}{s}\\
2.&10\,\frac{m}{s}\\
3.&15\,\frac{m}{s}\\
4.&20\,\frac{m}{s}\\
5.&25\,\frac{m}{s}\\
\end{array}$

In this problem I'm confused exactly which sort of information should I use?. Can someone help me with this matter?. I Think it has to do with $L = r\times p$ But I don't know if this is applicable to this given situation. Can someone help me here please?.
 

skeeter

Math Team
Jul 2011
3,363
1,854
Texas
Not clearly understanding what "The bar has a moment of $M = 3t$" means in this problem ...
 
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romsek

Math Team
Sep 2015
2,964
1,674
USA
What does it even mean the moment of the bar is M=3t
Why is the moment time varying?
 

romsek

Math Team
Sep 2015
2,964
1,674
USA
What does it even mean the moment of the bar is M=3t
Why is the moment time varying?
Oh it's obvious now. That blue disk is a grav plate that's linearly increasing ;)
 
Jun 2017
399
6
Lima, Peru
Any hint on how to solve this thing?. I'm assuming that it has to do with an area between the moment and time. I'm still stuck with this problem. Any help?