# physics

## Displacement,velocity and time

### Vectors and Scalars

• Vectors

• magnitude/size and direction
• displacement -- 5 meters to the right
• velocity -- 5/2 m/s to the right
• displacement = velocity * time
• Scalars

• magnitude/size
• distance -- 5 meters
• speed -- 5/2 m/s
• distance = speed * time
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### Calculating average velocity or speed

If Jun was able to travel 5km north in 1 hour in his car, what was his velocity?

Average velocity

Average speed or rate $$r=\frac{5km}{1 hour}$$ $$\quad=\frac{5km}{1 hour}*\frac{1000}{1}*\frac{m}{km}$$ $$\quad=5000*\frac{m}{hour}$$ $$\quad=5000*\frac{m}{hour}*\frac{1}{3600}*\frac{hour}{seconds}$$ $$\quad=1.39\frac{m}{s}$$

### Solving for time

Jun is running at a constant velocity of 3m/s to the east.

How long will it take him to travel 720 meters?

r: rate or speed, d: distance, t: time $$r=\frac{d}{t} \rightarrow t=\frac{d}{r}$$ $$t=\frac{720m}{3m/s}=240seconds$$

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$$\vec{v}:velocity \quad \vec{s}:displacement \quad t:time$$ $$\vec{v}=\frac{\vec{s}}{t} \rightarrow t=\frac{\vec{s}}{\vec{v}}$$ $$t=\frac{720m \quad east}{3m/s}=240seconds \quad east$$

### displacement from time and velocity

If Jun travels for 1 minute at 5 m/s to the south,

how much will he be displaced?

$$\vec{v}:velocity=5 m/s$$ $$\vec{s}:displacement$$ $$t:time=1minute$$ $$\vec{v}=\frac{\vec{s}}{t} \rightarrow \vec{s}= \vec{v}*t$$ $$\vec{s}= \vec{v}*t = 5\frac{m}{s}*1minute =5\frac{m}{s}*1minute*\frac{60}{1}*\frac{s}{minute} =300m \quad to \quad the \quad south$$