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Transcript
Review for Test 2 on Applications of Vectors PHY 621 1. An object is placed on an inclined plane. Frictional forces are present. a﴿ As the angle of the incline is increased, what happens to the magnitude of the following forces? FN Fg F_|_ F// Ff increases increases increases increases increases decreases decreases decreases decreases decreases remains constant remains constant remains constant remains constant remains constant b﴿ Which of the above force﴾s﴿ is/are independent of the angle of the incline? ________________ c﴿ Which of the above force﴾s﴿ is/are independent of the object’s mass? ___________________ 2. An object is being pushed along a horizontal surface by a force exerted at angle below the horizontal. Frictional forces are present. a﴿ As the angle below the horizontal is increased, what happens to the magnitude of the following forces? FN Fg Fay Fax Ff 3. increases increases increases increases increases decreases decreases decreases decreases decreases remains constant remains constant remains constant remains constant remains constant Fa An object is suspended by a wire such that the angle each “arm” of the wire makes the horizontal is different. The position of the object can be changed by sliding it to the left or right. As the object's position is adjusted , angle θ decreases while angle α increases. What affect does this have the following forces? Fg T1y T2y increases decreases remains constant increases increases decreases remains constant decreases remains constant Σ Ty increases Σ Tx increases decreases remains constant decreases remains constant T2 T1 θ α original T1 θ T2 α final Fnet x increases decreases remains constant Fnet y increases decreases remains constant 1 In class, Newton’s second law was stated simply but yet illustrates three important relationships. Identify the three relationships and the condition that must be met for each relationship to be demonstrated . 4. relationship condition _____________________________________________ __________________________ _____________________________________________ __________________________ _____________________________________________ __________________________ Use Newton’s first law of motion to explain why a bob, on a string, can be swung in a circle in a horizontal plane such that there is always tension in the string? Why doesn’t the bob just spiral into the centre of the circle? 5. __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ a﴿ Mr. Whitrow ﴾of mass 1.0 x 10 kg﴿ is sitting on a chair ﴾of mass 10 kg﴿. Rounding to the nearest integer, determine the following forces, including directions. F Whitrow on chair = ________________________ F chair on Whitrow = _________________________ F floor on chair = ___________________ F chair on floor = ___________________ b﴿ Does Newton’s third law apply to the above scenario? If so, why? If not, why? __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ 7. Refer back to question #4. When doing pushing/pulling problems in connected systems, which of the three relationships best describes why the force required to accelerate the whole system would be more than the force required to accelerate a single object in the system ﴾ex. the last person in line﴿? ____________________________________________________________________________________ ____________________________________________________________________________________ 2 PHY 621 1. Review for Test 2 on Applications of Vectors θ An object is placed on an inclined plane. Frictional forces are present. a﴿ As the angle of the incline is increased, what happens to the magnitude of the following forces? FN Fg F_|_ F// Ff increases increases increases increases increases decreases decreases decreases decreases decreases F = Fg cos θ F = -F F = Fg sin θ F =μF remains constant remains constant remains constant remains constant remains constant _|_ _|_ N // N f Fg = weight b﴿ Which of the above force﴾s﴿ is/are independent of the angle of the incline? ________________ none - all depend on the mass c﴿ Which of the above force﴾s﴿ is/are independent of the object’s mass? ___________________ 2. An object is being pushed along a horizontal surface by a force exerted at angle below the horizontal. Frictional forces are present. a﴿ As the angle below the horizontal is increased, what happens to the magnitude of the following forces? FN Fg Fay Fax Ff 3. increases increases increases increases increases decreases decreases decreases decreases decreases remains constant remains constant remains constant remains constant remains constant θ An object is suspended by a wire such that the angle each “arm” of the wire makes the horizontal is different. The position of the object can be changed by sliding it to the left or right. Refer the diagram shown. As the object is moved more to the left, angle θ decreases while angle α increases. What affect does this have on the following forces? Fg 0 N = Fg = increases decreases remains constant T1y increases T2y increases decreases remains constant decreases remains constant Σ Ty increases Σ Tx increases decreases remains constant decreases remains constant F netx increases F nety increases decreases remains constant decreases remains constant T1y = |T1| sin θ bigger bigger T1 T2 θ α T2y = | T2| sinα smaller smaller 3 In class, Newton’s second law was stated based on two important relationships. There are actually three different relationships that can be drawn from the law. Identify the three relationships and the conditions that must be met for each one. condition relationship 4. acceleration and mass are inversely proportional _____________________________________________ net force is held constant __________________________ mass is kept constant acceleration and net force are directly proportional__________________________ _____________________________________________ net _____________________________________________ force and mass are directly proportional 5. acceleration is constant __________________________ Use Newton’s first law of motion to explain why a bob, on a string, can be swung in a circle in a horizontal plane such that there is always tension in the string? Why doesn’t the bob just spiral into the centre of the circle? __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ 6. a﴿ Mr. Whitrow ﴾of mass 1.0 x 10 2 kg﴿ is sitting on a chair ﴾of mass 10 kg﴿. Rounding to the nearest integer, determine the following forces, including directions. - 981 N [up] F Whitrow on chair = ________________________ 981 N [up] F chair on Whitrow = _________________________ 1079 N [up] F floor on chair = ___________________ 100 kg 10 kg - 1079 N [up] F chair on floor = ___________________ b﴿ Does Newton’s third law apply to the above scenario? If so, why? If not, why? __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ 7. Refer back to question #4. When doing pushing/pulling problems in connected systems, which of the three relationships best describes why the force required to accelerate the whole system would be more than the force required to accelerate a single object in the system ﴾ex. the last person in line﴿? ____________________________________________________________________________________ ____________________________________________________________________________________ 4
