Solution - American Association of Physics Teachers
Solution - American Association of Physics Teachers Solution - American Association of Physics Teachers
2013 F = ma Exam 8The following information applies to questions 8 and 9A truck is initially moving at velocity v. The driver presses the brake in order to slow the truck to a stop. Thebrake applies a constant force F to the truck. The truck rolls a distance x before coming to a stop, and the timeit takes to stop is t.8. Which of the following expressions is equal the initial kinetic energy of the truck (i.e. the kinetic energy before thedriver starts braking)?(A) F x(B) F vt(C) F xt(D) F t(E) Both (a) and (b) are correctSolutionConsidering magnitudes only,K i = δK = W = F x9. Which of the following expressions is equal the initial momentum of the truck (i.e. the momentum before the driverstarts braking)?(A) F x(B) F t/2(C) F xt(D) 2F t(E) 2F x/vSolutionConsidering magnitudes only,butsop i = ∆p = F tx = 1 2 at2 = 1 2 (at)t = 1 2 vtp i = 2F x/vCopyright c○2013 American Association of Physics Teachers
2013 F = ma Exam 910. Which of the following can be used to distinguish a solid ball from a hollow sphere of the same radius and mass?(A) Measurements of the orbit of a test mass around the object.(B) Measurements of the time it takes the object to roll down an inclined plane.(C) Measurements of the tidal forces applied by the object to a liquid body.(D) Measurements of the behavior of the object as it floats in water.(E) Measurements of the force applied to the object by a uniform gravitational field.SolutionThe measurement described in (B) is certainly appropriate; the solid ball has a smaller moment of inertiathan the hollow sphere and will accelerate down the inclined plane faster.The measurements in (A) and (C) are unhelpful because they only probe the gravitational field outside theobject; for a spherically symmetric object this depends only on the mass. The force measured in (E) dependsonly on the object’s total mass; the buoyant force applied in (D) depends only on the external shape of theobject.Copyright c○2013 American Association of Physics Teachers
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2013 F = ma Exam 8The following information applies to questions 8 and 9A truck is initially moving at velocity v. The driver presses the brake in order to slow the truck to a stop. Thebrake applies a constant force F to the truck. The truck rolls a distance x before coming to a stop, and the timeit takes to stop is t.8. Which <strong>of</strong> the following expressions is equal the initial kinetic energy <strong>of</strong> the truck (i.e. the kinetic energy before thedriver starts braking)?(A) F x(B) F vt(C) F xt(D) F t(E) Both (a) and (b) are correct<strong>Solution</strong>Considering magnitudes only,K i = δK = W = F x9. Which <strong>of</strong> the following expressions is equal the initial momentum <strong>of</strong> the truck (i.e. the momentum before the driverstarts braking)?(A) F x(B) F t/2(C) F xt(D) 2F t(E) 2F x/v<strong>Solution</strong>Considering magnitudes only,butsop i = ∆p = F tx = 1 2 at2 = 1 2 (at)t = 1 2 vtp i = 2F x/vCopyright c○2013 <strong>American</strong> <strong>Association</strong> <strong>of</strong> <strong>Physics</strong> <strong>Teachers</strong>
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