What was his velocity when he began accelerating ?

[veena]

A runner accelerates to a velocity of 4.15 m/s due west in 1.5 s.His average acceleration is 0.640 m/s also directed to the west . What was his velocity when he began accelerating ?

 

[AbedeuS]

You can use the equation:

V_{final} = U_{initial} + at

Where:
V = Final Speed
U = Initial Speed
a = Acceleration (use your average acceleration)
t = Time across which the acceleration is applied

I will help you rearrange the equation if you need, but as the sticky suggests, this forum isn't here to give you homework answers, and most of the official PF helpers here will use an analogous equation to help guide you.

EDIT: Whoops got the equation a bit messed up there.

 

[veena]

yea but how ... thanks for ur help?

 

[AbedeuS]

Well acceleration speeds things up, reguardless of their initial velocity, in the equation, U is the initial velocity, and "at" is the amount the original velocity has increased by to get to the final velocity, acceleration multiplied by time equals the velocity increase, so the equation technically is

V_{final} = U_{initial} + X_{increase}​

Where "X" is the amount the initial speed has increased by to reach the final speed.