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## Homework Statement

1)a water tank has a rectangle base of area 5m x 4 m and is 3 m deep. if it is full of water, calculate the thrust on the base and on each side.

2)a model helicopter of mass 5 kg rises with constant acceleration from rest to a height of 60 m in 10 s. find the thrust exerted by the rotor blades during the ascent.

## Homework Equations

1)density= mass/ volume

pressure = force / area

2) s= (u+v)/t

v= ut + 1/2 at^2

## The Attempt at a Solution

1) weight of water when it is full = 1000 x (3 x4 x 5) = 60000 x 10 = 600000N

upthrust = P= F/A

on sides = 600000/12 = 50000N

base= 600000/ 20 = 30000 N [ ans : 5.9 x 10 ^5, 1.8 x 10 ^5, 2.2 x 10^5 N]

2) thrust force - weight = ma

60=v/2 (10)^2

v= 12 m/s

12= 1/2 (10)^2 a

a= 0.24 m/s^2

thrust force = 5 x 0.24 + 50 = 51.2 N [ans: 55]

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