# Problems with calculating the acceleration

## Homework Statement

A block moves 11 meters in 5 seconds on a straight line. Calculate the acceleration.

## Homework Equations

$v^2_x=v^2_{0x}+2a_x(x-x_0)$

$v_x=v_{0x}+a_xt$

$x=x_{0}+v_{0x}t+\frac{1}{2}a_{x}t^2$

## The Attempt at a Solution

$a_x=\frac{(\frac{11m}{5s})^2}{2\cdot 11m}=0.22m/s^2$

$a_x=\frac{(\frac{11m}{5s})}{5s}=0.44m/s^2$

$a_x=\frac{11m}{1/2\cdot (5s)^2}=0.88m/s^2$

Why am I getting 3 different answers? In my textbook, it lists the equations as being practically the same (straight-line motion with constant acceleration).

## Answers and Replies

lewando
Homework Helper
Gold Member
Assuming V0x = 0, then Vx ≠ 11/5 m/s.

1 person
Assuming V0x = 0, then Vx ≠ 11/5 m/s.

yes, V0x=0 because it starts at rest. But how do you know the velocity is not 11/5 m/s then?

lewando
Homework Helper
Gold Member
11/5 m/s is the average velocity. Vx is the instantaneous velocity at the 5m point.

1 person
11/5 m/s is the average velocity. Vx is the instantaneous velocity at the 5m point.

Ohhhh.
And because of that, I cannot use any of the formulas which includes the Vx therefore the only correct equation for my current problem is the 3rd, correct?

lewando
Homework Helper
Gold Member
Yes!

1 person