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A-Level Physics Mechanics Questions

A container rests on a top pan balance, which measures mass in kg. a funnel above the container holds some sand. The sand falls at a constant rate of 0.300 kg s-1 into the container, having fallen through an average vertical height of 1.60m.
(i) Show how the velocity of the sand as it lands in the container is 5.6 ms-1.
(ii) Calculate the magnitude of the momentum of the sand that lands in the container in each second.
(iii) The mass of the container is 0.650 kg. Show that the reading of the balance, 10.0s after the sand starts landing continuously in the container, will be 3.82kg. You may assume that the sand comes to rest without rebounding when it lands in the container.

I have figured out the first 2 parts to this question but the third part eludes me, any help would be appreciated.
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Avatar for Amefish
Amefish
20
Moved to physics
What've you tried and where are you getting stuck?
Original post by Jayc3
...


Sand mass after 10s = 3 kg. So 3 + 0.65 = 3.65 kg. Why isn't this the answer? Stationary vs moving mass; latter's momentum causes additional force to it's weight, hence a greater pan reading.

Add F = (change in mv)/(change in t) = (3 x 5.6)/10
For mass equiv, divide by g: (3 x 5.6)/(98.1) = 0.171 kg
So 3.65 + 0.171 = 3.82 kg
(edited 6 years ago)
Original post by Physics Enemy
.....
For mass equiv, divide by g: (3 x 5.6)/(98.1) = 0.171 kg
.....


I doubt this is correct. The unit does not match.
Original post by Eimmanuel
I doubt this is correct. The unit does not match.


Match what? Divide F by g to get m in kg.
Original post by Physics Enemy
Match what? Divide F by g to get m in kg.


Oh my bad, I saw 98.1 as 9.81. Sorry about it.

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