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Announcements. Homework for tomorrow… (Ch. 7, Probs 12, 16, & 20) Office hours… M 3-4 pm TWR 9-10 am F 1-2 pm Tutorial Learning Center – Houston Hall 113 MWR 8 am-6 pm T 8 am-7 pm F 8 am-5 pm. Chapter 7. Translational Momentum

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Announcements

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### Announcements

• Homework for tomorrow…

(Ch. 7, Probs 12, 16, & 20)

• Office hours…

M 3-4 pm

TWR 9-10 am

F 1-2 pm

• Tutorial Learning Center – Houston Hall 113

MWR 8 am-6 pm

T 8 am-7 pm

F 8 am-5 pm

## Chapter 7

Translational Momentum

(Impulse and Momentum Change)

### Review…

• Translational Momentum

• Newton’s 2nd Law for a particle

• … for a system of particle

Newton’s 2nd Law

solving for

and integrating

### Momentum Change andImpulse…

The momentum change an object experiences due to a collision is…

The impulse is equal to the area

under a force vs time graph

### Impulse-Momentum Theorem

The impulse of the force acting on an object equals the change in momentum of that object

Newton’s 2nd Law

Solving for

### Quiz Question 1

A 2 kg object is acted upon by a single force in the x-direction in a manner described by the graph shown. The momentum acquired by the object is?

• 16 kg·m/s

• 30 kg·m/s

• 32 kg·m/s

• 40 kg·m/s

• 48 kg·m/s

F(N)

12

8

4

t(s)

2

4

6

8

### Demonstration

Drop your favorite book on the floor from a height of 1 m…

What is the average force of the floor on the book?

Given: m = 1 kg, t = 10 ms

### Quiz Question 2

A person attempts to knock down a large wooden bowling pin by throwing a ball at it. The person has 2 balls of equal size and mass, 1 made of rubber and the other made of putty. The rubber ball bounces back, while the ball of putty sticks to the pin. Assume that the time interval for each collision is the same.

Which ball is most likely to topple the pin?

• the rubber ball

• the ball of putty

• makes no difference

### Prob 7.10

Until he was in his seventies, Henri LaMothe excited audiences by belly-flopping from a height of 12 m into 30 cm of water. Assuming that he reaches the bottom of the water and estimating his mass, find the magnitude of

• the average force

• the average impulse on him from the water.

### Demonstration

Will the egg break?