Answer:
C)
Explanation:
The buoyancy and weight of the wood have to be equal for the system to be in equilibrium. The total mass (then, weight) of the wood is the same, so the total buoyancy has to be the same. Since buoyancy is the weight of the liquid displaced, the volume of liquid displaced will be the same in either case, which means that the water level will remain unchanged.
1) First of all, let's find the resistance of the wire by using Ohm's law:
where V is the potential difference applied on the wire, I the current and R the resistance. For the resistor in the problem we have:
2) Now that we have the value of the resistance, we can find the resistivity of the wire
by using the following relationship:
Where A is the cross-sectional area of the wire and L its length.
We already have its length
, while we need to calculate the area A starting from the radius:
And now we can find the resistivity:
Solution:
We have,
Power [P] = 25000 Watt
Mass [m] = 6000 kg
Height [h] = 20 metres
Time [t] = ?
Now,
P = W/t = F x d/t = mxgx h/t
Or, 25000 = 6000 x 10 x 20/25000 [.......g = 10
m/s^2]
Or, t = 6000 x 10 x 20/25000
Or, t = 1200/25
Therefore, t = 48 second
Hence, the required time for the crane to lift the load is 48 seconds.