Question

When the body is travelling with constant velocity, the net force on it is zero.
A) True
B) False

Answer 1

Hint: When no change in velocity takes place then acceleration is also not acting because acceleration exists only when change in velocity occurs either velocity will decrease or increase. So applying Newton’s Law and we can easily identify the value of force acting on the body in this case.

Complete answer:
When the body is moving with some velocity then acceleration is acting on the body.
When velocity of the body is increasing then final velocity is greater than initial velocity in that case acceleration is positive. When velocity of the body is decreasing then final velocity is less than initial velocity in this case acceleration is taken as negative. So we can conclude that, positive sign of acceleration shows that velocity is increasing with time and the negative sign of acceleration shows that velocity is decreasing with time.
When velocity of the body is constant then acceleration is defined as zero because acceleration is defined as rate of change of velocity with respect to time.
Let us assume initial velocity of the body is u and final velocity of the body is v.
Acceleration can be represented Mathematically as ,
\[Acceleration=\dfrac{Change\_in\_velocity}{time}\]
Let us assume acceleration of the body is represented by a.
\[\Rightarrow \]\[a=\dfrac{v-u}{t}\](Equation 1)
According to the question, the body is moving with constant velocity, so magnitude of u and v is the same .Apply this in above Equation 1.So we get acceleration equal to zero.
\[\therefore a=0\]
According to Newton’s Second Law statement “Rate of change in momentum is directly proportional to external force applied” and from this statement we can derive that Force is equal to the product of mass and acceleration.
Mathematically this relation can be represented as,
 \[F=ma\]
Here Acceleration is equal to 0, we get
\[\therefore F=0\]
so no force will act on the body when it is moving with constant velocity.

So the given statement is true.

Note:
Here in this mathematical relation of acceleration we have to remember that velocity and acceleration both are vector quantity and direction of acceleration is not in the direction of velocity but it is taken as in the direction of change in velocity. This mathematical value of acceleration is the derived form of Newton’s Second Law.