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# Displacement with constant acceleration PowerPoint PPT Presentation

Displacement with constant acceleration. How far, how fast?. Review of v avg. We have seen a way to calculate v avg already: v avg = Δ x / t Let’s look at the Old School way to find an average…. Finding an average…. If you wanted to find the average of these numbers: 5,3,7 and 5

Displacement with constant acceleration

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## Displacement with constant acceleration

How far, how fast?

### Review of vavg

• We have seen a way to calculate vavg already:

vavg= Δx / t

• Let’s look at the Old School way to find an average….

### Finding an average…

• If you wanted to find the average of these numbers:

5,3,7 and 5

You would just add them up and divide by 4

Mmmk.

### Finding an average…

• You can do the same thing with velocities

• Suppose a car accelerates from 0m/s for 30 sec at 1m/s2.

That’s gonna take forever to do!

### Finding an average….

• OR… There’s a much easier way:

• If acceleration is constant (it always will be for us.) average the first and last velocities and you get the same answer.

Oh, good!

### Two equations

• We now have two ways to find vavg :

• Now let’s put them together…

Uhhhh…

• 1st:

### One equation

• 1st:

• Now, substitute in

• 2nd:

### One equation

• 1st:

• Now, substitute in

• 2nd:

• New Equation:

Ok, got it!

### Example

• A racing car reaches a speed of 42 m/s. It then begins a uniform negative acceleration, using its parachute and braking system, and comes to rest 5.5s later. Find the distance that the car travels during braking.

### Example

• A racing car reaches a speed of 42 m/s. It then begins a uniform negative acceleration, using its parachute and braking system, and comes to rest 5.5s later. Find the distance that the car travels during braking.

• Givens: vi=42 m/st= 5.5 s vf=0 m/sΔx= ?

### Example

• A racing car reaches a speed of 42 m/s. It then begins a uniform negative acceleration, using its parachute and braking system, and comes to rest 5.5s later. Find the distance that the car travels during braking.

• Givens: vi=42 m/st= 5.5 s vf=0 m/sΔx= ?

• Formula:

### Example

• A racing car reaches a speed of 42 m/s. It then begins a uniform negative acceleration, using its parachute and braking system, and comes to rest 5.5s later. Find the distance that the car travels during braking.

• Givens: vi=42 m/st= 5.5 s vf=0 m/sΔx= ?

• Formula:

### Practice

• For classwork, complete Practice C, Pg. 53