# CAS PY 211 Lecture Notes - Lecture 2: Minor Places In Arda, One Direction, Quadratic Equation

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Published on 6 Oct 2019

Department

Physics

Course

CAS PY 211

Professor

Answer to Essential Question 2.7: A common misconception is that the ball’s acceleration is zero

at the maximum-height point. In fact, the acceleration is , 9.8 m/s2 down, during the entire trip.

This is what is shown on the acceleration graph, for one thing – the graph confirms that nothing

special happens to the acceleration at t = 2.0 s, even though the ball is momentarily at rest. One

reason for this is that the ball is under the influence of gravity the entire time.

2-8 Solving Constant-Acceleration Problems

Consider one more example of applying the general method for solving a constant-

acceleration problem.

EXAMPLE 2.8 – Combining constant-acceleration motion and constant-velocity motion

A car and a bus are traveling along the same straight road in neighboring lanes. The car

has a constant velocity of +25.0 m/s, and at t = 0 it is located 21 meters ahead of the bus. At time t

= 0 , the bus has a velocity of +5.0 m/s and an acceleration of +2.0 m/s2.

When does the bus pass the car?

SOLUTION

1. Picture the scene – draw a diagram. The diagram in Figure 2.21 shows the initial

situation, the positive direction, and the origin. Let’s choose the positive direction to

be the direction of travel, and the origin to be the initial position of the bus.

2. Organize the data. Data for the car and the bus is

organized separately in Table 2.3, using subscripts

C and B to represent the car and bus, respectively.

Table 2.3: Summarizing the information that was given

about the car and the bus.

3. Solve the problem. Let’s use Equation 2.8 to write expressions for the position of

each vehicle as a function of time. Because we summarized all the data in Table 2.3

we can easily find the values of the variables in the equations.

For the car: .

For the bus: .

The bus passes the car when the vehicles have the same position. At what time does

? Set the two equations equal to one another and solve for this time (let’s call it t1).

Bringing everything to the left side gives: .

Chapter 2 – Motion in One Dimension Page 2 - 16

Figure 2.21: A diagram showing the initial

positions of the car and the bus, the position

of the origin, and the positive direction.

Car

Bus

Initial position

Initial velocity

Acceleration