Question

An Olympic track runner starts from rest and has an acceleration of 1.9 m/s2 for 3.7 s, then has zero acceleration for the remainder of the race. Find the runner's speed (in m/s) at the following times.

Answer 1

Answer:

a) t = 0    v = 0, b) t=3.7 s v = 7.03 m / s , c) t>3.7 s  v = 7.03 m / s

Explanation:

They ask us to find the speed of the runner for various times

a) when the race starts

         t = 0    v = 0

part of rest

b) for t = 3.7 s when acceleration ends

        v = v₀ + a t

        v = 0 + 1.9 3.7

        v = 7.03 m / s

c) for t> 3.7 s

     In this case the acceleration is zero a = 0

So its speed is constant

            v = 7.03 m / s

Answer 2

Answer:

• At rest:  speed = 0 m/s
• at 3.7 seconds:  speed = 7.03 m/s
• at zero acceleration( t greater than 3.7 ) : speed is constant = 7.03 m/s

Explanation:

The runner's speed from rest

V = u + at

u = initial speed

v = final speed

a = acceleration

t = time

At rest the runner's speed would be = 0 m/s

At 3.7 secs runner speed would be : v = u + at

                                                             v = 0 + (1.9 * 3.7)

                                                                = 7.03 m/s  

At acceleration = 0

zero acceleration = the speed remains constant = 7.03 m/s