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Understanding Pseudo Force

What is a pseudo force? Explain with the help of an appropriate example.

Solve the following problem using the concept of pseudo force:

Two rectangular blocks are stacked one over the other on a table. The lower and upper blocks have masses of 25 kg and 5 kg respectively. The coefficient of kinetic friction between the lower block and table is 0.3 and that between the two blocks is 0.6. A pulling force is applied to the lower block by means of a mass less rope attached to it.

a) Draw the free body diagram of the lower block "as seen" from the frame of reference of the table (or ground).

b) Draw the free body diagram of the upper block "as seen" i) from the frame of reference of the table (or ground), ii) from the frame of reference of the lower block.

c) At what acceleration of the lower block does the upper block start slipping relative to the lower block?

d) How much pulling force must be applied to the lower block to give it the acceleration calculated at c) above?

Solution Preview

Force is defined as an effort in the form of a push or pull applied on a body in order to change its state of rest or of uniform motion in a straight line. However, in an accelerated frame of reference this definition of force tends to break down. For example, when a vehicle accelerates suddenly, a passenger sitting in the vehicle is thrown back with a force. Nobody has pulled or pushed the passenger. In other words, no external force as defined above has been applied on the passenger; what then throws her back? The phenomenon is on account of a property of matter known as "inertia". Due to inertia the passenger has a tendency to continue to ...

Solution Summary

The concept of pseudo force has been explained in details. To illustrate the application of the concept, solution to a problem has been provided using the concept of pseudo force.

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