**Q.No.3.6: - Explain the circumstances in which the velocity v and acceleration a of a car are**

**(i) Parallel (ii) Anti-parallel (iii) Perpendicular (iv) v is zero but a is not zero. (v) a is zero but v is not zero.**

**Ans: -** **(i)** When the car is moving with increasing velocity then the direction of acceleration will be parallel to the velocity.

**(ii)** When the car is moving with decreasing velocity then the direction of acceleration will be anti-parallel to the velocity. ( the direction of velocity depends upon the change in displacement so when the body move slowly then it will move in the forward direction but change in displacement will be in the forward direction. On the other hand the direction of acceleration depends upon the direction of change in velocity and in this case the velocity of the car is decreasing so the direction of acceleration will be opposite to the direction of velocity)

**(iii)** When the car will move in a circle then the direction of velocity and acceleration will be perpendicular to each other. ( in this case the direction of velocity will be along the tangent to the circle and the direction of acceleration depends upon the change in velocity so if we take the vector sum then the resultant will always point toward the center of the circle so we can say that velocity and acceleration will be perpendicular to each other in this case )

**(iv)** When the brakes are applied on the moving car, it slows down and comes to rest due to negative acceleration in the opposite direction. Thus, velocity **v **is zero but **a **is not zero.

(v) When the car is moving with constant velocity then there will be no change in velocity so acceleration will be zero but velocity will not be zero.