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21. A car starts from rest and moves with a
uniform acceleration of 2 m/s². What will be
its velocity after it covers a distance of 49 m?
How much time will it take to cover the
distance of 49 m?


Sagot :

Sure, let's tackle this problem step by step, using kinematic equations from physics to find the velocity and the time required.

### Step 1: Understand Initial Conditions and Equations

1. Initial Conditions:
- The car starts from rest, so its initial velocity [tex]\( u \)[/tex] is 0 m/s.
- The acceleration [tex]\( a \)[/tex] is 2 m/s².
- The distance [tex]\( s \)[/tex] covered is 49 meters.

2. Equations Used:
- To find the final velocity ([tex]\( v \)[/tex]), we use the kinematic equation:
[tex]\[ v^2 = u^2 + 2as \][/tex]
- To find the time ([tex]\( t \)[/tex]), we use the kinematic equation:
[tex]\[ s = ut + \frac{1}{2}at^2 \][/tex]

### Step 2: Calculate Final Velocity

The car starts from rest, so [tex]\( u = 0 \)[/tex]. Substituting the values into the first equation:

[tex]\[ v^2 = 0 + 2 \cdot 2 \cdot 49 \][/tex]
[tex]\[ v^2 = 2 \cdot 2 \cdot 49 \][/tex]
[tex]\[ v^2 = 4 \cdot 49 \][/tex]
[tex]\[ v^2 = 196 \][/tex]
Taking the square root of both sides to solve for [tex]\( v \)[/tex]:

[tex]\[ v = \sqrt{196} \][/tex]
[tex]\[ v = 14 \text{ m/s} \][/tex]

So, the final velocity of the car after covering 49 meters is 14 m/s.

### Step 3: Calculate Time

Using the second equation and noting that [tex]\( u = 0 \)[/tex]:

[tex]\[ s = ut + \frac{1}{2}at^2 \][/tex]
[tex]\[ 49 = 0 \cdot t + \frac{1}{2} \cdot 2 \cdot t^2 \][/tex]
[tex]\[ 49 = \frac{1}{2} \cdot 2 \cdot t^2 \][/tex]
[tex]\[ 49 = t^2 \][/tex]
Taking the square root of both sides to solve for [tex]\( t \)[/tex]:

[tex]\[ t = \sqrt{49} \][/tex]
[tex]\[ t = 7 \text{ s} \][/tex]

So, the time it takes for the car to cover the distance of 49 meters is 7 seconds.

### Summary:

- The final velocity of the car after covering 49 meters is 14 m/s.
- The time it takes to cover this distance is 7 seconds.
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