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Physics: Post your doubts here!

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In one such pump the long approach pipe holds 500kg of water. A valve shuts when the speed of
this water reaches 2.0ms–1 and the kinetic energy of this water is used to lift a small quantity of
water by a height of 15m.
The efficiency of the pump is 10%.
Which mass of water could be lifted 15m?
A 0.15kg B 0.68kg C 1.5kg D 6.8kg
 
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In one such pump the long approach pipe holds 500kg of water. A valve shuts when the speed of
this water reaches 2.0ms–1 and the kinetic energy of this water is used to lift a small quantity of
water by a height of 15m.
The efficiency of the pump is 10%.
Which mass of water could be lifted 15m?
A 0.15kg B 0.68kg C 1.5kg D 6.8kg

Answer:

I guess,
K . E= 1/2 x m x v2(squared)
= 1/2 x 500 x 2 (2)
=1000 J

then,
G.p.e = mgh
re-arrange to
m= G.p.e/( g x h)
=1000J / (9.81 x 15 )
= 6.8kg


6.8kg for 100%
m1 kg for 10%
cross multiply to get 0.68kg so answer is B.
 
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Solve this please... Answer is C. I get A :p
You get diameter 4.81mm so for radius d/2 and convet mm to m.
In m 4.81/2/1000
Next u find the volume using 4/3pi r^3
Density =mass(kg)/volume(m^3)
Convert g to kg 0.450/1000 ÷vol and you get C as the answer.
 
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You get diameter 4.81mm so for radius d/2 and convet mm to m.
In m 4.81/2/1000
Next u find the volume using 4/3pi r^3
Density =mass(kg)/volume(m^3)
Convert g to kg 0.450/1000 ÷vol and you get C as the answer.
Thanks! i forgot to calculate radius and was recklessly using value of D in the formula (4/3)*pi*r^3
 
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Well i am not sure if this is the question you're talking about (I could only find this component for 2017 March). If so, the answer is C. Three forces in equilibrium forms a closed triangle. Since the weight of the object is 10N and the angle is 90 degrees, by using Pythagoras theorem Weight = (F1^2 + F2^2)^(1/2). ''C' and 'D' only satisfies this equation. Now if you compare the angle between the vertical line and the rope of F1 attached to the object, you will notice that F1 makes greater angle than F2. With smaller angle, Value of Cos theta increases hence force also increases (F = R*Cos theta). So F2 has greater force
 

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