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Unformatted text preview: magalhaes (bam2734) – Homework #4 – Erskine – (58200) 1 This print-out should have 26 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A certain force with units of measure M L T 2 is given by the equation F = K M L 2 T 4 , where M is a mass, L is a length, T is a time and K is a constant. What are units of the constant K ? 1. [ K ] = T 6 M 2 L 2 2. [ K ] = M 2 L 2 T 6 3. [ K ] = L T 2 4. [ K ] = T 2 M L 5. [ K ] = T 2 L correct 6. [ K ] = M L T 2 Explanation: Solving for K , K = F T 4 M L 2 Since the dimensions of force are [ F ] = M L T 2 , we get [ K ] = parenleftbigg M L T 2 parenrightbigg T 4 M L 2 = T 2 L 002 10.0 points Despite a very strong wind, a tennis player manages to hit a tennis ball with her racquet so that the ball passes over the net and lands in her opponent’s court. Consider the following forces: 1. A downward force of gravity, 2. A force by the hit, and 3. A force exerted by the air. Which of the above forces is (are) acting on the tennis ball after it has left contact with the racquet and before it touches the ground? 1. 1 and 3. correct 2. 2 and 3. 3. 1, 2, and 3. 4. 1 and 2. 5. 1 only. Explanation: The forces acting on the tennis ball after it has left contact with the racquet are gravity and air resistance. A force by the hit is no longer acting on the ball. 003 10.0 points You place a box weighing 332 . 6 N on an in- clined plane that makes a 39 . 5 ◦ angle with the horizontal. Compute the component of the gravita- tional force acting down the inclined plane. Correct answer: 211 . 56 N. Explanation: Basic concepts θ W θ θ W W 1 The component of the gravitational force acting down the plane is the side opposite the angle θ , so W 1 = W sin θ 004 10.0 points magalhaes (bam2734) – Homework #4 – Erskine – (58200) 2 An object Q has a mass M Q and an acceler- ation vectora Q . Another object P of twice the mass has twice the magnitude of acceleration in the same direction as object Q. What is true about summationdisplay vector F for object P vs object Q? 1. summationdisplay vector F P has the same magnitude but op- posite direction from summationdisplay vector F Q . 2. summationdisplay vector F P has twice the magnitude of summationdisplay vector F Q , in the same direction. 3. summationdisplay vector F P has four times the magnitude of summationdisplay vector F Q , in the same direction. correct 4. summationdisplay vector F P has the same magnitude and di- rection as summationdisplay vector F Q . Explanation: summationdisplay vector F Q = M Q a Q and summationdisplay vector F P = (2 M Q )(2 a Q ) = 4 summationdisplay vector F Q ....
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