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Unformatted text preview: Activity 9 FBD Newton's Laws - Friction 2/19/07 M1 = 1 kg Coefficient of kinetic friction between M1 and the surface is 0.20. The pulley is massless and frictionless. Use g = 10 m/s2. 1. Find the accelerations of the blocks. What is the tension in the string? M2 = 3 kg Notes: 1. Draw a FBD of all the forces acting on each block. 2. Redraw the diagram and simplify it. 3. Write out Newton's 2nd law for EACH block SEPARATELY in each direction. 4. Solve equations. Treat each block separately. What joins them is that they have the SAME acceleration (and velocity). The direction has to be consistent. If you choose to the right of M1 along the surface to be positive, then the downward direction for M2 needs to be positive. n (?) T2 (60 N) 30 37 w (160 N) T1 (100 N) 2. Find the components of the forces that are not along the x- and y directions. 2. Redraw the FBD showing all the forces (along the x- and y-direction). 3. Find the normal force (force on mass by surface) 4. What is the acceleration of the mass along the surface if the coefficient of sliding friction between the two surfaces is 0.3? 3. A person pushes a lawn mower up an incline as shown below. Determine the magnitude of the kinetic friction force of the surface on the 20-kg lawn mower. The coefficient of kinetic friction between the mower and the lawn is 0.30 and the 300-N force of the person on the mower is horizontal. What is the lawn mower's acceleration? (Use g = 10 m/s2)
1. Draw a FBD showing all the forces. 2. REDRAW the picture showing all the forces along the x-direction (along the ramp) and y-direction (perpendicular to the ramp). Be sure this is a SIMPLIFIED drawing. 3. Write out Newton's 2nd Law for each direction. Be sure to include an expression for WHAT the net force is, not just F = ma. 4. Solve equations 37 ...
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