# lecture8 - Friction is given by μ k m θ F A Example...

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Newton’s Laws (III) Newton’s Laws (III) Blocks on ramps, and other problems Serway and Jewett : 5.7, 5.8

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Doing problems with “F=ma” Draw the free-body diagram carefully. You may need to know the direction of a from kinematics, before considering forces (for friction). Any axes will do, but some choices make the algebra simpler – set up equations for each direction. You need one (scalar) equation for each (scalar) unknown, in general (but, the mass will often cancel out).
Example : Show that the contact forces are equal F A

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Accelerated motion Example : A block slides down a ramp, with friction m θ v Assume m, , μ k are known, and find the acceleration.
Accelerated motion Example : A block is pushed with a force F A at an angle to the horizontal, find the acceleration.

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Unformatted text preview: Friction is given by μ k. m θ F A Example Obtain an expression for the stopping distance for a skier moving down a slope with friction with an initial speed of v 1 . Find the distance given that μ k =0.18, v=20m/s and θ=5.0º. θ d Increasing θ so that , the block slips, from which we get: f n mg s μ This is an easy method of measuring max θ= max tan μ= s Question : Can we calculate μ s ? M m θ Frictionless surfaces, ideal pulleys, etc. For what angle θ is the system in equilibrium? Summary Problems using Newton’s Second Law: Set up free-body diagram, then and solve. , a F m = ∑ Practice Problems : Chapter 5 Problems: 43, 46 (ans: 31.7-48.6N ), (5 th ed) Problems 49, 53...
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lecture8 - Friction is given by μ k m θ F A Example...

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