# KVPY Interview Important Questions Physics Part 3

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Q: 21. What is terminal velocity and derive the expression for terminal velocity of the body in the, above setup

Sol. When a body is dropped in a viscous fluid, it is first accelerated and then its acceleration becomes zero and it attains a constant velocity called terminal velocity. Diagram of Terminal Velocity Diagram of Terminal Velocity

(i) Effective force acting downward

(ii) viscous force acting upward

Since the ball is moving with a constant velocity v there is no acceleration in it, the net force acting on it must be zero. That is

or

Thus, terminal velocity of the ball is directly proportional to the square of its radius

Q: 22. How will you measure acceleration due to gravity at any place on the earth?

Sol. With the help at a simple pendulum

Q: 23. Derive an expression for the time period of a simple pendulum. Period of a Simple Pendulum Diagram of Period Of a Simple Pendulum

Q: 24. When two infinite parallel wires carrying current in same direction are placed vacuum, then will they experience

Sol. Yes they experience force at attraction

Q: 25. Give the name and formula of that force?

Sol. Force per unit length of wire Lorentz force Length of Wire Lorentz Force Diagram of Length of Wire Lorentz Force

Q: 26. A block of mass ‘m’ is placed on the table and another block of mass ‘M’ is hanging from a pulley and these two masses are connected by a string. All surfaces are frictionless. Find acceleration of the system Two Masses Connected by a String Diagram of Block of Mass from a Pulley and these two Masses are Connected by a String

A=b by string constant Acceleration of the System Find Acceleration of the System Acceleration of theS Second System Find Acceleration of the Second System

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