Question

Sarah is running a race and is almost to the finish line. In the last 5 seconds, her velocity changes from 2m/s to 4m/s. What is her average acceleration during the last 5 seconds of the race?

Answer 1

Solution :-

Here

Initial velocity = 2 m/s

Final velocity = 4 m/s

Time = 5 sec

v = u + at

4 = 2 + a(5)

4 - 2 = a(5)

2 = 5a

2/5 = a

Hence, acceleration is 2/5 m/s²

Answer 2

`\boxed {\boxed {\sf a= \frac {2}{5} \ or \ 0.4 \ m/s^2}}`

Step-by-step explanation:

Acceleration is found by dividing the change in velocity by the time. The formula is:

`a= \frac {v_f-v_i}{t}`

where
`v_f` is the final velocity,
`v_i` is the initial or starting velocity, and
`t` is the time.

Her velocity changes from 2 meters per second to 4 meters per second in the 5 seconds. Therefore:

`v_f= 4 \ m/s \\v_i= 2 \ m/s \\t=5 \ s`

Substitute the values into the formula.

`a= \frac { 4 \ m/s- 2 \ m/s}{5 \ s}`

Solve the numerator and subtract.

`a= \frac { 2 \ m/s}{5 \ s}`

Divide.

`a= (2)/(5) \ m/s/s= (2)/(5) \ m/s^2`

This can also be written as a decimal.

`a=0.4 \ m/s^2`

Her average acceleration during the last 5 seconds of the race is 2/5 or 0.4 meters per square second.