Physics 121, Sections 9, 10, 11, and 12 Lecture 7 Today's Topics Homework 3: Due Friday Sept 23@ 6: 00PM Ch.3:#64,75,and81 Ch4:#4,8,21,25,36,and40 Chapter 4: Motion in 2-D Projectile motion Relative velocity More examples of FBD's Physics 121: Lecture 7, Pg 1
Physics 121: Lecture 7, Pg 1 Physics 121, Sections 9, 10, 11, and 12 Lecture 7 Today’s Topics: Homework 3: Due Friday Sept. 23 @ 6:00PM Ch.3: # 64, 75, and 81. Ch.4: # 4, 8, 21, 25, 36, and 40. Chapter 4: Motion in 2-D Projectile motion Relative velocity More examples of FBD’s
Typical questions (projectile motion; for given Vo and e) What is the maximum height the ball reaches(h)? P y: h=(vo sin 0)t-1/2 gt2 v=(Vo sin 0)-gt=0 at P 0 (Vo Sin 0)/g L How long does it take to reach maximum height? y (vo sin 0)/g Would the answers above be any different if the h projectile was moving only along y-axis(1-D motion with the initial velocity Vo sin(0)? (A) YES (B)NO(C)CANT TELL Vo sin(0)X Physics 121: Lecture 7, Pg 2
Physics 121: Lecture 7, Pg 2 Typical questions : (projectile motion; for given v0 and q) What is the maximum height the ball reaches (h) ? How long does it take to reach maximum height ? h = (v0 sin q) t - 1/2 g t2 v = (v0 sin q) - g t = 0 at P t = (v0 sin q) / g t = (v0 sin q) / g ! y : q h L y x v0 P Would the answers above be any different if the projectile was moving only along y-axis (1-D motion) with the initial velocity: v0 sin (q) ? ( A ) YES ( B ) NO ( C ) CAN’T TELL h y v0 sin(q) x P
Typical questions (projectile motion; for given vo and 0) What is the range of the ball (L)? h xo t=(vo cos 0)t 0 X How long does it take for ball to reach final point(P)? y: y=(vo sin 0)t/1/2 gt2=01 when at P [(Vo sin 0)-12gt]t=0 t=0 t=2(vo sin 0)/g Physics 121: Lecture 7, Pg 3
Physics 121: Lecture 7, Pg 3 Typical questions : (projectile motion; for given v0 and q) What is the range of the ball (L) ? How long does it take for ball to reach final point (P) ? q h L y x v0 P y = (v0 sin q) t - 1/2 g t2 = 0 ! when at P [ (v0 sin q) - 1/2 g t] t = 0 t = 0 ; t = 2 (v0 sin q) / g L = vx0 x : t = (v0 cos q) t y :
Problem 1 Suppose a projectile is aimed at a target at rest placed at the same height. at the time that the projectile leaves the cannon the target is released from rest and starts falling toward ground. Would the projectile miss or hit the target (A)MISS (B)HIT (C)CANT TELL PROJECTILE t=0 t=0 TARGET y Physics 121: Lecture 7, Pg 4
Physics 121: Lecture 7, Pg 4 Problem 1 Suppose a projectile is aimed at a target at rest placed at the same height. At the time that the projectile leaves the cannon the target is released from rest and starts falling toward ground. Would the projectile miss or hit the target ? t = t1 y x v0 t = 0 t = 0 TARGET PROJECTILE ( A ) MISS ( B ) HIT ( C ) CAN’T TELL
Problem 2 Suppose a projectile is aimed at a target at rest somewhere above the ground as shown in Fig below. At the same time that the projectile leaves the cannon the target falls toward ground. Would the projectile miss or hit the target? (A)MISS (B)HIT (C)CANT TELL t=0 TARGET t=t, t=0 PROJECTILE Physics 121: Lecture 7, Pg 5
Physics 121: Lecture 7, Pg 5 Problem 2 Suppose a projectile is aimed at a target at rest somewhere above the ground as shown in Fig. below. At the same time that the projectile leaves the cannon the target falls toward ground. Would the projectile miss or hit the target ? t = t1 q y x v0 t = 0 t = 0 TARGET PROJECTILE ( A ) MISS ( B ) HIT ( C ) CAN’T TELL