**
SPH 4U1**

**
Physics Grade 12**

**
Unit 2: Kinematics (How Things Move)**

**
Note 3: Acceleration & Acceleration Due to
Gravity**

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Reference Text Sections 1.2, 1.3

*Recall Definitions:*

**Acceleration **– rate of change of velocity

**Instantaneous Acceleration** – acceleration at one
point in time

*DEMO: heavy and light objects accelerating at same
speed. Discuss Aristotles’ mistakes and Galileo’s discovery….*

* *

**Gravity – **force of attraction between masses

**Acceleration Due to Gravity** – Approx. 9.8 m/s^{2}

**Free Fall** – motion of an object falling to earth
with only gravity acting on it.

**Terminal Speed** – Air resistance becomes so great
that there is no more acceleration.

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Solving** Constant** Acceleration Problems (the formulas
to use J):

These can be derived from Velocity vs Time graph

**Example 1:**

Find a baseball’s acceleration if the pitcher’s wind up is 3m and the speed is 50 m/s.

Solution:

Rearrange

**Example 2:**

A steel ball is thrown from the ledge of a building so that it has an initial velocity of magnitude 15.0 m/s. The ledge is 15.0 m above the ground (assume no air resistance).

a) What are the total flight time and the speed of impact at the ground if the initial velocity is upward? (Answer: flight time = 3.86 s, impact speed = 22.8 m/s)

b) What are these two quantities if the initial velocity is downward?

(Answer: flight time = 0.8 s, impact speed = 22.8 m/s)

c)
Based on your answers to a) and b), write a concluding statement.(*Answer to
this will be the final velocity is independent of whether the ball is thrown up
or down)*

**Example 3:**

Car A is traveling at 11 m/s [N] when it passes a
stationary Car B. When A is 20m ahead of B, B begins to accelerate at a uniform
rate of 4.0 ms^{-2} [N] and at the instant, A begins to accelerate at a
uniform rate of 2 ms^{-2} [S]. Determine when and where B catches up
with A.