Question 1.3: Automobile Traveling at a Curved Road A car of mass m is goi......

The centrifugal force is expressed in the form

F_c=\frac{m V^2}{r}            (1.11)

Introducing the given data,

F_c=\frac{2000(42.5)^2}{120}=30,104  kg \cdot m / s ^2=30.1  kN

Comment: Since the automobile moves at constant speed along its path, the tangential component of inertia force is zero. Centrifugal force (normal component) represents the tendency of the car to leave its curved path.

Power is defined as the time rate at which work is done. Note that, in selecting a motor or engine, power is a much more significant criterion than the actual amount of work to be performed. When work involves a force, the rate of energy transfer is the product of the force F and the velocity V at the point of application of the force. The power is therefore defined thus:

\text { Power } \quad P=F V       (1.12)

In the case of a member, such as a shaft rotating with an angular velocity or speed \omega in radians per unit time and acted on by a torque T, we have:

\text { Power } \quad P=T \omega       (1.13)

The mechanical efficiency, designated by e, of a machine may be defined as follows:

e=\frac{\text { Power ouput }}{\text { Power input }}        (1.14)

Because of energy losses due to friction, the power output is always smaller than the power input. Therefore, machine efficiency is always less than 1. Inasmuch as power is defined as the time rate of doing work, it can be expressed in units of energy and time. Hence, the unit of power in SI is the watt (W), defined as the joule per second (J/s). If US customary units are used, the power should be measured in ft · lb/s or in horsepower (hp).