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Tutor profile: Priydevvrat S.

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Priydevvrat S.
Aerospace engineer by profession. Tutor by passion.
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Questions

Subject: Python Programming

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Question:

Write a function using turtle object to draw a circle at a given position(x,y) with a given radius. The function should draw the specified circle by moving by 1 deg along the circumference.

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Priydevvrat S.
Answer:

import turtle import math def drawCircle(t,x,y,radius): t.penup() t.home() # for going to origin(0,0) t.setpos(x+radius,y) # setting pen position to right most point of circle. t.setheading(90) # This rotates the pen direction by 90 deg t.pendown() # Start drawing t.color('red') distance = 2*math.pi*radius/360 # 360 parts of circle circumference for i in range(360): t.left(1) # rotate by 1 deg to left t.forward(distance) t.penup() #turtle.done() def main(): t = turtle.Turtle() # turtle object x = 50 # centre x coordinate y = 75 # centre y coordinate radius = 100 drawCircle(t,x,y,radius) main()

Subject: Aerospace Engineering

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Question:

Why does a launch vehicle take off vertically instead of going at an angle?

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Priydevvrat S.
Answer:

The main reason lies in minimizing the fuel expenditure. When an object moves with respect to the atmosphere, a resistance force called "drag" acts on the object (common example: during cycling or running, you need to put more effort to move forward when you are going against the wind). To move against this drag force, additional energy is spent. This comes at a cost (extra fuel) since it is an additional weight that needs to be carried in the rocket. The atmosphere extends up to about 100 km above the Earth's surface. In outer space (above 100 km), there is no air and hence no drag force. To minimize the duration for which this drag force acts on the body, the wise choice is to cross the atmosphere as soon as possible, which is achieved by moving straight up. Another reason for this comes from the structural point of view. Most of the rocket geometry is cylindrical and stages are stacked upon each other. When the rocket is moving straight up, the drag force is symmetric about the body and does not create a moment which might cause a structural failure.

Subject: Physics

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Question:

How is it possible for current to flow instantaneously in a circuit (the light bulb glows immediately as you press the switch, doesn't it?) when drift velocity of electrons is so small?

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Priydevvrat S.
Answer:

Electric current is the flow of electrons in metal wires. Electrons move in the wire at the drift velocity $$v_d$$ which is given by $$ v_d = \frac{𝐼}{ne𝐴} $$ where $$I$$ is the electric current, $$n$$ is the electron number density in the metal of the wire, $$e$$ is the electric charge on the electron and $$A$$ is the cross sectional area of the wire. Drift velocities are typically of the order of a few $$cm~s^{-1}$$. Free electrons are present throughout the metal wire (in conductors). When circuits is turned on, electromagnetic waves arise as a result of voltage difference across the circuit. These waves travel with the speed of light and sets all the electrons into motion, all along the wire. The information about beginning of the flow of current is transmitted through the propagation of these waves and not with drift velocity of electrons. Individual electrons need not travel throughout the wire for current to start flowing. So, even though individual electrons drift slowly along the wire, current transmission is quasi-instantaneous (with speed of light).

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