Physics 113 –Summer 2008

Participation Points #4

To be turned in at the end each discussion session, stapled on top of Participation Points #3, #2, and #1

 


Student’s name _____________________           Total previous points accumulated:

 

 

 

 

 

 

 

 

 

 

 

9.1-       Momentum of the center of mass. A 1000 kg car at velocity v1=2.5 i + 10 j m/s skids on a frictionless icy road, it hits a 500 kg wagon moving at v2=  4 i + j m/s. If they stay together, what is their velocity?

 

 

 

 

 

 

 

 

9.2-       Inelastic collision. A 1000 kg car moving at 10 km/h collides with a 1500 kg car moving in the same direction at 5 km/h. The slower car is equipped with spring bumpers with spring constant 20kN/m. Find the maximum compression of the spring.

 

 

 

 

 

 

 

 

9.3-       Elastic collision. While playing a ball in the street, a child accidentally tosses a ball at 20m/s toward the front of a car moving toward him at 15 m/s. What is the speed of the ball after it rebounds elastically from the car?

 

 

 

 

 

 

 

 

 

 

10.1-     Torque. A torque of 100Nm is required to start a revolving door. If a child can push 50N North while the door is aligned in the SW direction, how far from the axis of rotation must he apply this force?

 

 

 

 

 

 

 

10.2-     Analog of Newton’s Law. A 2.5kg block rests on a 300 slope and attached by a negligible mass string to a solid drum of mass 1kg and radius 5cm. When released, the block accelerates down the slope at 2m/s2. What is the coefficient between block and slope?

 

 

 

 

 

 

 

 

 

10.3-     Rolling motion. A round object like a sphere or wheel may be characterized by a rotational inertia of the form I=αMR2, with  α a constant. Derive an expression for the final speed of such an object if it starts from rest and rolls without slipping down an incline of vertical height h.

 

 

 

 

 

 

 

 

11.1-       Vector cross product. Find a force vector that when applied at the point x=2m, y=1m, will produce a torque τ=5 k Nm about the origin.

 

 

 

 

 

 

 

11.2-    Angular momentum. A 5cm diameter baseball has a mass of 100g and is spinning at 200 rad/s. What is the magnitude of its angular momentum?

 

 

 

 

 

 

 

11.3-    Conservation of angular momentum. A turntable of radius 20cm and rotational inertia 0.01kg.m2 is spinning freely at 20rpm about its central axis, with a 20g mouse on its outer edge. The mouse walks from the edge to the center, find the new rotation speed.