1. Instructor: Dr. Tatiana Erukhimova
Physics 218: Mechanics
Instructor: Dr. Tatiana Erukhimova
Lecture 20

2. Impulse
Changes in a particle’s momentum are due to impulse, which depends on the time over which the net force acts.

3. Impulse
Suppose you throw a ball with a mass of 0.4 kg against a brick wall. It hits the wall moving horizontally to the left at 30 m/s and rebounds horizontally to the right at 20 m/s. a) Find the impulse of the net force on the ball during its collision with the wall. b) If the ball is in contact with the wall for s, find the average horizontal force that the wall exerts on the ball during the impact.

4. Quiz
A small car weighing mc is traveling due north when it collides with a pick-up truck weighting mt which was traveling due east. After the collision the two vehicles move off together at an angle θ north of east. The driver of the car claimed that the truck driver was at fault because he was exceeding the speed limit, going with a velocity vt. If this were true, what was the car’s initial velocity, vc?

5. Polar coordinates

6. A ball of mass m is swung around a circle at the end of a string of length L. The string will break if the tension in it exceeds a critical value, Tc. What is the largest constant angular velocity the ball can have without breaking the string?

7. A ball of mass m is swung around a circle at the end of a string of length L. What is the minimum  the ball can have and still travel in a circle without string becoming slack?

8. Have a great day! Reading: Chapter 12
Hw: All Chapter 12 problems and exercises