Answer:
13 m/s
Explanation:
Given average acceleration a and initial velocity v0 we can compute the final velocity using the equation
a = (v - v0)/t where t is the time taken to reach final velocity from initial velocity
Here a = 2 m/s² and v0 is the initial velocity when she passes her younger brother v0 = 5m/s.
It takes t = 4 s to pass her older brother at which time her speed is v, say
Then
a = (v - v0)/t
Plugging in known values,
2 = (v - 5)/4
Switch sides:
(v- 5)/4 = 2
Multiply both sides by 4:
v - 5 = 8
v =5 + 8 = 13 m/s - the speed at which she passes her older brother
