Physics 113 –Morning 2012

Extra credits problems #2

Due June 7, 2012

Team #______________

Member 1__________________

Member 2__________________

Member 3__________________

Rules:

-Collaboration between team members is encouraged, each member will be responsible for one problem and may be asked to explain it.

-Each member should present the solution on a blank sheet with her/his name on it; solutions from each team are to be stapled together

-Solutions should include “self-explained” diagrams/sketches, with minimal wording. Presentation will count toward the problem grading.

1.- Using results from the method to calculate the height of the lecture room using a stopwatch and a quarter, estimate the force exerted by your hand in Newton (N) on the quarter through detailed steps with equations and reasonable estimates of intermediate variables.

2.- A 2inx4inx8ft wood bar is leaning against the wall, draw a free-body diagram of forces on it. Give an expression through detailed steps using the diagram what would be the minimum angle of the wood bar with the floor so it won’t slide.

3.- The friction force always opposes a motion, it is F_f=µ_sN, where N is the normal force exerted by the surface on the box. From the second Newton’s Law, the average force applied on an object can be written as

, from here . The quantity is the impulse. So the change of linear momentum of an object equals the impulse it received. I will call this the linear momentum balance. 1)Starting from the linear momentum balance, derive the 1D kinematic equation #1 for the box as it slides on the rough surface 2)Using a camera, explain a method to calculate the coefficient of kinetic friction between the box and the surface 3)Explain what may be a problem you would need to overcome when you perform this experiment.

Explain a method to calculate the coefficient of static friction µ_s between a box and a surface.