Question

A woman walked 115 m. As she did so, her speed increased from 4.20 m/s to 5.00 m/s. How long did it take her to walk this distance?

Answer 1

25 seconds

Step-by-step explanation:

Assuming the woman is accelerating at a constant rate of
`a \;\;m/s^2` from the initial velocity, u=4.20 m/s, to the final velocity, v=5.00 m/s.

Let she takes t seconds to cover the distance, s=115 m.

As acceleration,
`a=(v-u)/(t)=(5-4.2)/(t)`

`\Rightarrow at=0.8\cdots(i)`

Now, from the equation of motion

`s=ut+\frac 12 at^2`

`\Rightarrow s=ut+\frac 12 at(t)`

`\Rightarrow 115=4.2t+\frac 12 * 0.8 t` [ from equation (i)]

`\Rightarrow 115=(4.2+0.4)t`

`\Rightarrow t= 115/4.6 = 25` seconds.

Hence, she takes 25 seconds to walk the distance.