Question

A sprinter accelerates from the starting block to a speed of 8.0 m/s in 4.0 s. What is the magnitude of the sprinter’s acceleration?

A. 12.0 m/s

B. 2.0 m/s2

C. 2.0 m/s

D. 12.0 m/s2

Answer 1

The acceleration is defined as the ratio between the change in speed and the change in time (i.e. the time elapsed to perform the speed change).

In this case, the reference to the "starting block" hints that the initial speed is 0, and the final speed is 8 m/s. This means that the change in speed is 8-0=8 m/s.

We are given that this change in speed takes place in 4 seconds.

So, the acceleration is the ratio between the change in speed and the time elapsed: 8/4=2m/s^2

Answer 2

The correct answer is B.

Step-by-step explanation:

First, we must identify the data of the problem:

`V_(0)`: Initial speed.

V: Final speed.

a: Acceleration.

t: Time.

Using the cinematic formula:

V =
`V_(0)` + a * t

We cleared the incognita a:

a =
`(V - V_(0) )/(t)`

Since the sprinter starts from rest, we consider
`V_(0)` = 0
`(m)/(s)`.

So when we replace the data in the equation we are left:

a =
`(8 (m)/(s) - 0 (m)/(s)  )/(4 s)`

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

Have a nice day!