Question

At the starting gun, a runner accelerates at 1.9 m/s2 for 5.2 s. The runner’s acceleration is zero for the rest of the race. What is the speed of the runner at t = 2.0 s?

Answer 1

Answer: 3.8m/s

Explanation: he accelerates 5.2s ,but we know that:

vf=vo+at , vo=0  , t=2s  so : vf = 1.9*2 = 3.8m/s

Answer 2

Answer:

$3.8\text{m}/ \text{s}^2$

Explanation:

Given: At the starting gun, a runner accelerates at 1.9 m/s2 for 5.2 s. The runner’s acceleration is zero for the rest of the race.

To Find:  the speed of the runner at t = 2.0 s.

Solution:

initial speed of runner($\text{u}$) = $0$ $\text{m}/ \text{s}^2$

acceleration for first 5.2s of race=  $1.9$ $\text{m}/ \text{s}^2$

to find speed of runner at , $\text{t}=2\text{s}$

Using first equation of motion,

$\text{v}=\text{u}+\text{at}$

putting values in the equation

$\text{v}=0+1.9\times2$

$\text{v}=3.8$ $\text{m}/ \text{s}^2$

So,

The speed of the runner at $\text{t}=2\text{s}$, is $3.8\text{m}/ \text{s}^2$