Chapters

 page 4

This text is meant to accompany class discussions. It is not everything there is to know about the forces. It is meant as a  prep for class. More detailed notes and examples are given in the class notes, presentations, and demonstrations (click here.)

 When solving these problems ALWAYS Draw a freebody for EVERY object. Sum up the force in the x and y directions. Don't try to make a shortcut. Do the work.

Example 7
• Question
• Solution
• Video Solution

An 8.0 kg box is sliding at the bottom of an incline at 5.00 m/s. The box will slow to a rest. If the coefficient of friction is 0.600, how far up the incline will the box travel?

This video can be found on YouTube at http://youtu.be/rAXcUH_JwUY

 Example 7: Moving with a Net Acceleration Question Solution Video Solution Two boxes are on the incline as shown. What is the net force for each box? This video can be found on YouTube at http://youtu.be/hL4_W_TYIak

 Example 8: Sliding down an incline while accelerating
• Question
• Solution
• Video Solution
 A box starts from rest and accelerates as it slides 1.15m down the incline shown below. The incline is 34 degree from horizontal. The coefficient of kinetic friction is 0.350 and the coefficient of static friciton is 0.450. What is the speed of the box when it reaches the bottom of the incline?

The coefficient of kinetic friction was choosen because the box is sliding across the surface. If the box was at rest then the coefficient of statics friction whould have been used.

This is waht your paper would look like. You do not have to write the force questions.

• Is it on a planet? Yes, therefore is experiences weight.
• Is there a contact surface? Yes. therefore there is anormal force.
• Is there friction? Yes, therefore it experiences friction.
• Is there drag? No.
• Is there a rope? No.
• Other forces? No.

 This video can be found on YouTube at http://goo.gl/1OTrcs

Example 9
• Question
• Solution
• Video Solution
 The sign has a mass of 100 kg. The beam has a weight of 1350 N. Where the beam attaches to the wall, the connection has an upward force of 1520 N.

Hopefully you noticed how every solution involved drawing a freebody diagram and summing up the forces.

by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)