midterm practice exam 2 solutions

# Physics for Scientists and Engineers (3rd Edition)

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PHY131 Midterm-II Practice Exam Solutions 1) A 1.50 m long board with a mass of 80.0 kg is leaning against a wall. The angle between the horizontal ground and the board is 60 0 . Assume that there is no friction between the board and the wall, but the board is firmly set against the ground.What is the force the wall exerts on the board (magnitude and direction)? θ F F W F mg l y x O Since there is no friction between board and wall, F W has no vertical component. In static equilibrium the net torque around point O is: N 226 tan 2 mg F cos 2 mg sin F 0 cos 2 l mg sin lF W W W = θ = θ = θ = θ θ 2) A 5.00 g bullet is fired horizontally into a 1.5 kg block resting on a horizontal surface. The coefficient of kinetic friction between the block and the surface is 0.2. The bullet remains embedded into the block, which is observed to slide 0.250 m along the surface before stopping. What was the initial speed of the bullet? s m 300 x g 2 m M m v x g 2 M m x g ) M m ( 2 ' v ' v ) M m ( 2 1 K x F W g ) M m ( F ' v m M m v p p ; ' v ) M m ( p ; mv p k k k 2 fr fr k fr after before after before = µ + = µ = + + µ = + = = = + µ = + = = + = = 3) Four small masses of m = 2.50 kg each are rigidly arranged on a “pinwheel” as shown below.

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