Acceleration Formula for Physics (velocity and time)


In this article, we will look at the acceleration formula with velocity and time. 
Before going any further let us define what is acceleration.
Acceleration is change in velocity over time
There are two ways to find acceleration 

  • using velocity
  • using force formula

In this article, we will look at the formula for acceleration with velocity and time. We use the formula of acceleration with velocity and time when we do not have any knowledge of force acting on the body. We only have information about

  • Change in velocity
  • Time

Acceleration formula with velocity and time

As mentioned earlier acceleration is the change in velocity over time. So acceleration is the change in velocity divided by time. Mathematically,
acceleration formula
If,
  • \(v_1\) is the initial velocity
  • \(v_2\) is the final velocity and
  • \(t\) is the time taken to reach ending or final velocity from starting or initial velocity then

formula for acceleration
Here,
  • acceleration \(a\) is in \(m/s^2\)
  • velocities \(v_f\) and \(v_i\) are in \(m/s\)
  • \(\Delta v\) is short form for change in velocity.
  • and time \(t\) is in \(seconds\) 

Acceleration formula important facts

  1. Acceleration s a vector quantity. Acceleration has both magnitude (a value) and direction
  2. The direction of acceleration can be different from the direction of velocity.
  3. Unit of acceleration is \(m/s^2\)
  4. Acceleration can be negative and positive. It is negative when velocity decreases with time. It is positive when velocity increases with time.

Solved Questions on formula of acceleration

Question 1. A bus decreases its speed from \(80\,\,m\,s^{-1}\) to \(60\,\,m\,s^{-1}\) in 5 seconds. Find the acceleration of the bus.
Solution. Here it is given that
initial velocity,
\(v_i=80ms^{-1}\)
and final velocity,
\(v_f=60ms^{-1}\)
Time \(t=5\,s\)
We have to calculate the acceleration from this data. Now from accelration formula we have
\[a=\frac{v_f-v_i}{t}\]
putting in the respective values 
\[a=\frac{(60-80)ms^{-1}}{5s}=-4ms^{-2}\]
Note that the answer is negative. This negative sign indicates that velocity is decreasing with time.

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