Explanation :
The forces acting on hot- air balloon are:
Weight, (W)
Force due to air resistance, (F)
Upthrust force, (U)
Its weight W is acting in downward direction. The upthrust force U acts in upward direction. When the balloon is moving upward, the air resistance is in downward and vice versa.
In this case, the hot-air balloon descends vertically at constant speed.
so, 
and 
so,
....................(1)
when it is ascending let the weight that it is releasing is R, so
..........(2)
solving equation (1) and (2)

2F is the weight of material that must be released from the balloon so that it ascends vertically at the same constant speed.
Answer:
497.00977 N
3742514.97005
Explanation:
= Density of water = 1000 kg/m³
C = Drag coefficient = 0.09
v = Velocity of dolphin = 7.5 m/s
r = Radius of bottlenose dolphin = 0.5/2 = 0.25 m
A = Area
Drag force

The drag force on the dolphin's nose is 497.00977 N
at 20°C
= Dynamic viscosity = 
Reynold's Number

The Reynolds number is 3742514.97005
Answer:
Open circuit
Explanation:
An open circuit is simply an electrical circuit that is not complete. In such a circuit, there is a gap and this will not allow the electric current to pass through.
Despite all the elements being complete in the circuit, an open circuit will halt the flow of electric current and will not do deliver the necessary energy it is supposed to.
In such a circuit, the wires are cut of and not connected properly.
The reverse is a closed circuit.
Answer:
upthrust or BUOYANT FORCE =Vdg
volume=LWH
upthrust=(4cm×5cm×2cm)×1g/cm²×g
upthrust=40cm³×1g/cm³×g
upthrust=40gf or 0.04kg×10m/s²=0.4N
weight of the displaced liquid is upthrust.
so mass=40g or 0.04kg
upthrust=40gf or 0.4Nand mass of the displaced liquid=40g or 0.04kg
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