The one that will change the velocity of a periodic wave is : 
B. Changing the medium of the wave
Waves is always determined by the properties of the medium, which means that changing the medium will change the velocity of the wave
hope this helps
        
                    
             
        
        
        
Answer:
false statement : b )  For the motion of a cart on an incline plane having a coefficient of kinetic friction of 0.5, the magnitude of the change in kinetic energy equals the magnitude of the change in gravitational potential energy
Explanation:
mechanical energy = potential energy + kinetic energy = constant 
differentiating both side 
Δ potential energy + Δ kinetic energy = 0 
Δ potential energy = -  Δ kinetic energy
first statement is true. 
Friction is a non conservative force so inter-conversion of potential and kinetic energy is not possible in that case. In case of second  option,  the correct relation is as follows 
change in gravitational potential energy = change in kinetic energy + work done against friction . 
So given 2 nd  option is incorrect. 
In case of no change in gravitational energy , work done is equal to 
change in kinetic energy. 
 
        
             
        
        
        
The ampere (symbol: A) is the SI base unit of electric current equal to one coulomb per second.
The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 times 10–7 newton per meter of length.
Electric current is the time rate of change or displacement of electric charge.
One ampere represents the rate of 1 coulomb of charge per second.
The ampere is defined first (it is a base unit, along with the meter, the second, and the kilogram), without reference to the quantity of charge.
The unit of charge, the coulomb, is defined to be the amount of charge displaced by a one ampere current in the time of one second.
This is your answer friend. Hope it helps you.
 
        
             
        
        
        
Answer:
a)  μ = 0.475
, b)   μ = 0.433
Explanation:
a) For this exercise of Newton's second law, we create a reference system with the x-axis parallel to the plane and the y-axis perpendicular to it
X axis
      Wₓ - fr = m a
the friction force has the expression
      fr = μ N
y Axis
      N -  = 0
 = 0
let's use trigonometry for the components the weight
      sin 27 = Wₓ / W
      Wₓ = W sin 27
      cos 27 = W_{y} / W
      W_{y} = W cos 27
      N = W cos 27
      W sin 27 - μ W cos 27 = m a
      mg sin 27 - μ mg cos 27 = m a
       μ = (g sin 27 - a) / (g cos 27)
       very = tan 27 - a / g sec 27
       μ = 0.510 - 0.0344
       μ = 0.475
b) now the block starts with an initial speed of 3m / s. In Newton's second law velocity does not appear, so this term does not affect the result, the change in slope does affect the result
          μ = tan 25 - 0.3 / 9.8 sec 25
          μ = 0.466 -0.03378
          μ = 0.433