Consider the following equations of kinematics. v xf = v xi + a x t v x,avg = vx

Question

Consider the following equations of kinematics.

vxf = vxi + axt

vx,avg = vxi + vxf/2

xf = xi + 1/2(vxi + vxf)t
xf = xi + vxit + 1/2 axt2

vxf2 = vxi2 + 2ax(xf xi)xf =

(a) Can the equations of kinematics be used in a situation in which the acceleration varies in time?

Yes or No    

(b) Can they be used when the acceleration is zero?

Yes or No

2) Two cars are moving in the same direction in parallel lanes along a highway. At some instant, the velocity of car A exceeds the velocity of car B. Does this mean that the acceleration of A is greater than that of B?

Yes or No    

Explain your answer.

Explanation / Answer

Part(a)No they cant be used when acceleration varies with time.Because all these results have been derived when acceleration is constant.

Part(b)Yes when acceleration is zero then these equations can be used.Because here acceleration is constant.

Part(c)No .Actually it depends on initial velocity of cars along with accelaration.

So acceleration alone will not be deciding factor for comparison of velocities at any instant.Initial velocities also need to be taken in account.

As Vf =Vi +at

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