PHYSICS 50: Lecture 3.1 RICHARD CRAIG

Plan for the day Chapter 3 Free fall in two dimensions Horizontal rifle shot Discussion Baseball hit Relative Velocity 1-D 2-D Quiz (Again!!!) Information sheet Circular motion

Homework #2 Read Chapter 3: Sections 1,2,3 Exercises and Problems:2.42, 2.83, 3.9, 3.16, 3.27, Due Thursday, 2/7

X and Y motion are Separable The red ball is dropped, and the yellow ball is fired horizontally as it is dropped. The strobe marks equal time intervals.

2-D Motion: Horizontal Gun Shot A hunter holds a rifle horizontal and shoots. The gun is 1.5m high and the bullet leaves the gun with a velocity of 350m/s. Assume no air resistance and a flat surface. How far will the bullet travel before it hits the ground? What will be the bullets velocity (vector) when it hits the ground?

How to solve a physics problem 1. Diagram/Sketch of situation: Insert coordinate system 2. Identify initial conditions: Include in diagram 3. Identify target variable: Include in diagram 4. Find relevant equations 5. Solve 1. One equation / one unknown (plug and chug) 2. One equation / two unknowns (help! Need more equations!) 3. Two equations / two unknowns (very common for what we call “hard” problems) 6. Think 1. Answer makes sense? 2. Units on answer 3. Number of significant figures

Projectile motion: 2-D A projectile is any body given an initial velocity that then follows a path determined by the effects of gravity and air resistance. Begin neglecting resistance.

The equations of motion under constant acceleration

3-D Motion: Baseball hit A batter hits a baseball 60m/s at an angle 30 degrees above horizontal. Assume the ball is 1.0m high when it is hit. Neglect air friction. How far from home plate does the ball land?

Tranquilizing the falling monkey

A projectile is launched at a 30° angle above the horizontal. Ignore air resistance. The projectile’s acceleration is greatest Q3.10 A. at a point between the launch point and the high point of the trajectory. B. at the high point of the trajectory. C. at a point between the high point of the trajectory and where it hits the ground. D. misleading question — the acceleration is the same (but nonzero) at all points along the trajectory E. misleading question — the acceleration is zero at all points along the trajectory Concept Question 1

Relative velocity on a straight road—passing!

Flying to the right or wrong airport

The pilot of a light airplane with an airspeed of 200 km/h wants to fly due west. There is a strong wind of 120 km/h blowing from the north. If the pilot points the nose of the airplane north of west so that her ground track is due west, what will be her groundspeed? A. 80 km/h B. 120 km/h C. 160 km/h D. 180 km/h E. It would impossible to fly due west in this situation. Q3.12 Concept Question #2

Circular Motion When you go around a curved road at constant speed are you accelerating? 1)Is your speed changing? 2)Is your direction changing?

Figure 3.28a

Figure 3.28b

Figure 3.28c

Determination of the centripetal acceleration Uniform circular motion and projectile motion compared and contrasted. For uniform circular motion, the acceleration is centripetal a c = v 2 /R (radial inward).