The answer is C.
Say you are pulling on a rope that goes over one frictionless pulley. You are essentially moving the mass but in a different direction than gravity, so there is no advantage or disadvantage.
The free body diagram of the bas is shown below:
The torque is given by:

where F is the force and:

is the perpendicular distance between the rotation axis and the line of action of the force, which we called the moment arm. We know that the torque follows the principle of superposition then to find the total torque we need to add the torque each force exert. Before we do this we need to find the correct sign of the torque so we need to remember that if a force makes an object rotate counterclockwise then the torque is positive; otherwise it is negative. In this case Force two will exert a positive torque while the other two forces acting on the bar exert a negative torque.
For force one and the weight the moments arms are 5 m and 2.5 m, respectively. This comes from the fact that the forces are perpendicular to the rod.
For force two the moment arm is given as:

Hence the total torque is given by:

Therefore, the total torque on the bar is -3.9 Nm (this means that the bar will rotate clockwise).
From x = 1.0 m to x = 4.25 m, displacement = 3.25 m
Average velocity of crawling of baby = 0.226 m/s
We know that time taken = Displacement/Time
= 
= 14.38 seconds
So, the baby will take a time of 14.38 seconds from x=1.0m to x=4.25m at an average velocity of 0.226 m/s.
Answer: 
Explanation:
Given
The frequency of the source is 
Change in frequency is 
Speed of sound 
Suppose
is the velocity of the observer
Doppler frequency is given by

Here, the source is at rest
While approaching source, frequency is

While leaving, frequency is

The difference in the frequency is
