Subhankar Roy: Your Educational Guide

Answer

Let the Total age of 10 persons be x,

Given Avg. age of 10  persons = 60, hence we can say x/10 = 60, or x = 60*10 = 600

Now also given that total age of 8 persons = 488

Therefore , total age of 2 persons = 600 - 488 = 112

Hence , Avg, age of 2 persons = 112 / 2 = 56 years.

Answer

Let the number of books bought for Rs.60 were x,

Hence cost of 1 book is 60/x

Now if he bought x+5 books for Rs. 60 then cost of each book would have been Re. 1 less,

So , According to problem, 

60/x -60/(x+5) = 1

Solving this we get x =15 , -20. So x =15 is the actual number of books since -20 is not possible.

Answer

The basic operational voltage equation of a DC motor is : E= Eb + Ia*Ra Where Eb is the back emf generated when the motor is running. Ra is the armature resistance. Ia is the armature current. E is the Emf. Hence resistance can be written as : Ra =(E-Eb)/Is Now, since the motor is at rest in the beginning, the back emf Eb is 0. Hence the resistance is Ra =E/Ia , thus the resistance is low during motor starting time.

Answer

Velocity can be simply stated as the speed at which a given object is moving in a particular direction. Velocity is a vector quantity hence whenever we mention it we need to mention its direction also.

Mathematically we can define velocity as V= s/t, where 's' is the displacement of an object and 't' is the total time taken for achieving the displacement 's'.

One thing to keep in mind is that displacement and distance are not the same, So while solving problems it may happen that an object returns to it's original position (starting point) , say after covering a distance of 40 km in a given path, in such cases displacement will be 0 hence velocity will also become 0 but distance will remain 40 km and hence speed will not be equal to 0. But this does not mean that the velocity was always 0, in other words we need to find the instantaneous velocity of that object.

The Unit of velocity is similar to that of speed , i.e.., m/s (meter per second) , miles / hr (miles per hour) , km/ hr (kilometer per hour) ,etc.