Physics – Chapter 2, Section 2

St. Augustine Preparatory SchoolAugust 24, 2015

Previously…

Vave = (xf-xi)/(tf-ti)

aave = (vf-vi)/(tf-ti)

We are going to add a few more formulas to our list today

Displacement with Constant Acceleration

• We can use this formula to find displacement if the acceleration is constant, but not known:

Example question: When Maggie applies the brakes of her car, the car slows uniformly from 15.0m/s to 0.00m/s in 2.50s. How many meters before a stop sign must she apply her brakes to stop in time?

Finding final velocity with constant acceleration

• We can use this formula to find final velocity if the acceleration is constant and known:

vf = vi + aΔt

• Example: An automobile with an initial speed of 4.30m/s accelerates uniformly at the rate of 3.00m/s2. Find the final speed after 5.0s.

Displacement with Constant Acceleration

• We can use this formula to find displacement if the acceleration is constant, but known:

Note: the time is squared at the end

Final velocity after any displacement

• If the initial velocity, acceleration and displacement are known, we can calculate the final velocity without knowing the time:

• Remember when solving for square roots, you will get both a positive and negative answer. You have to decide which to keep

Example

• A person pushing a stroller starts from rest, uniformly accelerating at a rate of 0.500 m/s2. What is the velocity of the stroller after it has travelled 4.75m.

Practice Problems

• Page 49: 1, 4• Page 51: 3, 4• Page 54: 1-6