An olympic class sprinter starts a race from rest with an acceleration of 4.8 m/s2. take her direction of motion as the positive direction.

The question is incomplete, the complete form is:

An Olympic class sprinter starts a race from rest with an acceleration of . Take her direction of motion as the positive direction.

(a) What is her speed 2.40 s later?

(b) Sketch a graph of her position vs. time for this period.

The answer is:  

a) What is her speed 2.40 s later?

Her speed is 11.52 m/s

Explanation:

The speed can be determined by means of the kinematic equation that corresponds to a Uniformly Accelerated Rectilinear Motion.

 (1)

Where is the initial velocity, a is the acceleration and t is the time.

Since she starts the race from rest her initial speed will be zero ()

(a) What is her speed 2.40 s later?

By means of equation 1 it is gotten:

Hence, her velocity is 11.52 m/s

(b) Sketch a graph of her position vs. time for this period.

The position of that period can be known by means of the next equation:

(2)

However, the initial speed is equal to zero, so equation 2 can be rewritten:

 (3)

But the acceleration is equal to

(4)

Then, equation 4 can be used to sketch a graph of her position vs. time.

For t = 0 s

For t = 1 s

For t = 1.40 s

For t = 2 s

For t = 2.40 s

hi there!

out of the two, (b) precision would be more reasonable.   however, both a and b could be pretty reasonable.

-awesomerepublic   : )

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