Well I may be wrong as I've not done Physics for a while, but here are my tips, so hopefully they help 
. Unsure whether you want help just for the first question or for this entire question, so sorry.
For the first question note how Background Radiation is always present. Considering the graph, you will say that it plateaus over time, and flattens off. At this point we can deduce that the substance itself has near completely decayed: but there's still a large count per minute, and that must be from background radiation, as it's always present. So considering the height where it plateaus, that's gotta be the Background rad.
For question number two, your effectively redrawing the graph but without the BR. So measure the CPM of each cross, subtract the BR, and replot it with a curved line if best fit. The plateau where we found the BR should now be near merged with the x axis.
Lastly, we can see the place where it is now below 25 CPM with our newly plotted line. Considering the error interval of ± 5 CPM, when do we know that it is safe to drink?
Hope that helps! Wishing you luck
. Unsure whether you want help just for the first question or for this entire question, so sorry.
For the first question note how Background Radiation is always present. Considering the graph, you will say that it plateaus over time, and flattens off. At this point we can deduce that the substance itself has near completely decayed: but there's still a large count per minute, and that must be from background radiation, as it's always present. So considering the height where it plateaus, that's gotta be the Background rad.
For question number two, your effectively redrawing the graph but without the BR. So measure the CPM of each cross, subtract the BR, and replot it with a curved line if best fit. The plateau where we found the BR should now be near merged with the x axis.
Lastly, we can see the place where it is now below 25 CPM with our newly plotted line. Considering the error interval of ± 5 CPM, when do we know that it is safe to drink?
Hope that helps! Wishing you luck
Original post by {Moss}
Well I may be wrong as I've not done Physics for a while, but here are my tips, so hopefully they help
. Unsure whether you want help just for the first question or for this entire question, so sorry.
For the first question note how Background Radiation is always present. Considering the graph, you will say that it plateaus over time, and flattens off. At this point we can deduce that the substance itself has near completely decayed: but there's still a large count per minute, and that must be from background radiation, as it's always present. So considering the height where it plateaus, that's gotta be the Background rad.
For question number two, your effectively redrawing the graph but without the BR. So measure the CPM of each cross, subtract the BR, and replot it with a curved line if best fit. The plateau where we found the BR should now be near merged with the x axis.
Lastly, we can see the place where it is now below 25 CPM with our newly plotted line. Considering the error interval of ± 5 CPM, when do we know that it is safe to drink?
Hope that helps! Wishing you luck
. Unsure whether you want help just for the first question or for this entire question, so sorry.
For the first question note how Background Radiation is always present. Considering the graph, you will say that it plateaus over time, and flattens off. At this point we can deduce that the substance itself has near completely decayed: but there's still a large count per minute, and that must be from background radiation, as it's always present. So considering the height where it plateaus, that's gotta be the Background rad.
For question number two, your effectively redrawing the graph but without the BR. So measure the CPM of each cross, subtract the BR, and replot it with a curved line if best fit. The plateau where we found the BR should now be near merged with the x axis.
Lastly, we can see the place where it is now below 25 CPM with our newly plotted line. Considering the error interval of ± 5 CPM, when do we know that it is safe to drink?
Hope that helps! Wishing you luck
Thank you 😊
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