August 29, 2007 - Department of Physics



TA: Tomoyuki Nakayama Monday, February 8th, 2010

PHY 2048: Physic 1, Discussion Section 3081

Quiz 3 (Homework Set #5)

Name: UFID:

Formula sheets are not allowed. Calculators are allowed. Do not store equations in your calculator. You need to show all of your work for full credit.

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A can of bolts and nuts is pushed 2.00 m along an x axis by a broom along the greasy (frictionless) floor of a car repair shop in a version of shuffleboard. Figure below gives the work W done on the can by the constant horizontal force from the broom, versus the can’s position x. The scale of the figure’s vertical axis is set by Ws = 9.00 J.

a) What is the magnitude of that force?

According to the graph, the work done by the applied force is Ws = 9 J when the displacement is d = 2 m. The definition of work gives

Ws = Fd ⇒ F = Ws/d = 4.50 N

b) If the can was initially at rest and had a mass of 0.500 kg, what is its speed at the end of the 2.00 m?

We apply the work-kinetic energy theorem to the can at x = 0 m and x = 2 m, express the kinetic energy in terms of mass and velocity, and solve the equation for the velocity.

ΔK = (1/2mvf2)– 0 = Ws ⇒ v = √(2Ws/m) = 6.00 m/s

c) If the can had an initial kinetic energy of 5.00 J, moving in the positive direction of the x axis, what is its kinetic energy at the end of the 2.00 m?

Now the initial kinetic energy is not zero. The work-kinetic energy theorem yields

ΔK = Kf – Ki = Ws ⇒ Kf = Ki + Ws = 14.0 J

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