Physics 2210
Lecture 11
Today’s Concept: Inelas;c Collisions Mechanics Lecture 11, Slide 1 Recap
P~tot =
X
mi~vi
i
Mechanics Lecture 11, Slide 2 ACT
A wood block rests at rest on a table. A bullet shot into the block stops inside, and the bullet plus block start sliding on the fric;onless surface. The momentum of the bullet plus block remains constant Before AEer A) Before the collision. B) During the collision C) AEer the collision D) All of the above E) Only A and C above Mechanics Lecture 11, Slide 3 Mechanics Lecture 11, Slide 4 CheckPoint
Suppose you are on a cart ini;ally at rest that rides on a fric;onless track. If you throw a ball off the cart towards the leE, will the cart be put into mo;on? LeE Right A) Yes, and it moves to the right. B) Yes, and it moves to the leE. C) No, it remains in place. Mechanics Lecture 11, Slide 5 CheckPoint
Suppose you are on a cart which is ini;ally at rest that rides on a fric;onless track. You throw a ball at a ver;cal surface that is firmly aVached to the cart. If the ball bounces straight back as shown in the picture, will the cart be put into mo;on aEer the ball bounces back from the surface? LeE Right A) Yes, and it moves to the right. B) Yes, and it moves to the leE. C) No, it remains in place. Mechanics Lecture 11, Slide 6 ACT
Suppose you are on a cart that is moving at a constant speed v toward the leE on a fric;onless track. If you throw a massive ball straight up (rela;ve to the cart), how will the speed of the cart change? LeE Right v
A) Increase B) Decrease C) Will not change Mechanics Lecture 11, Slide 7 Mechanics Lecture 11, Slide 8 CheckPoint
Two balls of equal mass are thrown horizontally with the same ini;al velocity. They hit iden;cal sta;onary boxes res;ng on a fric;onless horizontal surface. The ball hi_ng box 1 bounces back, while the ball hi_ng box 2 gets stuck. Which box ends up moving faster? A) Box 1 B) Box 2 C) same 1 2 Mechanics Lecture 11, Slide 9 ACT
Two equal-­‐mass balls swing down and hit iden;cal bricks while traveling at iden;cal speeds. Ball A bounces back, but ball B just stops when it hits the brick. Which ball is more likely to knock the brick over? A B A) A B) B C) They both have the same chance. Mechanics Lecture 11, Slide 10 Ballistic Pendulum
m
v
M
H
A projec;le of mass m moving horizontally with speed v strikes a sta;onary mass M suspended by strings of length L. Subsequently, m + M rise to a height of H. Given H, what is the ini;al speed v of the projec;le? Mechanics Lecture 11, Slide 11 Mechanics Lecture 11, Slide 12 Breaking it down into steps
before m
during aEer v
v
M
H
splat Which quan;;es are conserved before the collision? A) momentum B) mechanical energy C) both momentum and mechanical energy
Mechanics Lecture 11, Slide 13 Breaking it down into steps
before m
during aEer v
v
M
H
splat Which quan;;es are conserved during the collision? A) momentum B) mechanical energy C) both momentum and mechanical energy
Mechanics Lecture 11, Slide 14 Breaking it down into steps
before m
during aEer v
v
M
H
splat Which quan;;es are conserved aEer the collision A) momentum B) mechanical energy C) both momentum and mechanical energy
Mechanics Lecture 11, Slide 15 Mechanics Lecture 11, Slide 16