Answer:
The frequency of the waves depends on the distance between wave fronts - considering a front as a maximum disturbance of the wave
(Consider the waves emitted by an organ pipe: condensation and rarefactions)
The waves themselves are a fixed distance apart -
as one moves towards the source the waves received will be closer together (higher frequency)
So if the frequency received increases, the distance between the source and the observer must be decreasing
The only vertical forces are weight and normal force, and they balance since the surface is horizontal. The horizontal forces are the applied force (uppercase F) in the direction the block slides and the frictional force (lowercase f) in the opposite direction.
Apply Newton's 2nd Law in the horizontal direction:
ΣF = ma
F - f = ma
where f = µmg
F - µmg = ma
F = m(a +µg)
F = (20 kg)(1.4 m/s² + 0.28(9.8 m/s²)
F = 83 N
Answer:
The slower the train is moving, the less are the changes of the magnetic flux, thus the eddy currents become weaker.
Explanation:
A magnetic brakes is not a very efficient way of braking when a train is moving slowly because at low speeds, the changes in the magnetic flux are very less and so it causes the eddy current to become weaker.
Let us find the drag force which is proportional to the velocity of two conducting plates.
The EMF that is induced in the eddy currents are : 
The force which is due to the induced magnetic field is, 
Therefore, 

Here, force is directly proportional to the velocity of the two conducting plates.
Therefore, we can say that when the speed of the train is low, the magnetic flux changes are less and thus the eddy currents are weaker.
Answer:
Rice
Explanation:
Bro just dip it in rice thatd the only way to go
<span>Carnot cycle efficiency = work done/heat supplied = (Th - Tc)/Th
where, Th is temperature of hot reservoir and Tc is temperature of cold reservoir.
we have given the values as Heat supplied = 1.3 MJ or 1300 KJ, Th = 427 degree C and Tc = 90 degree C.
converting degree Celsius to kelvin temperatures, Th = 427 + 273 = 700 K
Tc = 90 +273 = 363
solving equations, (700 - 363)/700 = work done / 1300
work done = 625.86 KJ i.e. 0.626 MJ work is done .</span>