A stationary source S generates circular outgoing waves on a lake. The wave speed is 4.0 m/s and the crest-to-crest distance is 80 cm. A boat is approaching the source at 1.0 m/s. The frequency of these waves, as observed by a person in the boat, is A. 3.2 Hz. B. 3.8Hz. C. 6.3 Hz. D. 6.7 Hz. E. 5.0 Hz.

correct option is C.

Explanation:

As the source is stationary. And the observer is moving towards the source. It leads to Doppler effect. The frequency measure by the observer will be higher as is it moving towards the source. Lets find out the value of frequency.

The formula for this case is,

where

= c/λ

λ = wavelength

by putting it in above equation,

v = c/λ ( 1+ v/c)

  =

   = 6.3 Hz.

So the correct option is C.

wavelength divides in half and speed stays the same.

weight of the box is given as

here this is placed on the inclined of angle 42 degree

now this weight will have two components one is along the incline other is perpendicular to it

so here we need to apply a force parallel to incline opposite to its component of weight

so here the component of weight is given as

here we have

so it requires 75 n force to move it upwards