A side view of a child’s tricycle with rubber tires on a horizontal concrete sidewalk. If a string were attached to the upper pedal on the far side and pulled forward horizontally, the tricycle would start to roll forward. (a) Instead, assume a string is attached to the lower pedal on the near side and pulled forward horizontally as shown by A. Will the tricycle start to roll? If so, which way? Answer the same questions if (b) the string is pulled forward and upward as shown by B, (c) if the string is pulled straight down as shown by C, and (d) if the string is pulled forward and downward as shown by D. (e) What If? Suppose the string is instead attached to the rim of the front wheel and pulled upward and backward as shown by E. Which way does the tricycle roll? (f) Explain a pattern of reasoning, based on the figure, that makes it easy to answer questions such as these. What physical quantity must you evaluate?

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James SamasLv8

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Video text description for the Direct Measurement Video of Newton’s Second Law – Fan Cart In this video, a small cart that has a mass of 600 grams rests on a table top. There is a fan on top of the cart, blowing air backwards at a steady rate. A stretched spring is attached to the back of the cart by a string, holding it in place. A scale, marked off in newtons, is positioned next to the spring and a small dot at the end of the spring indicates the magnitude of the spring force. The spring and scale together is called a “dynamometer.” Before the cart is released from the spring, the dynamometer reads approximately 1.9 newtons. The video is recorded at 60 frames per second, resulting in playback motion 2 times slower than normal. A frame counter indicates the current frame. A horizontal distance scale, marked off in centimeters, is also shown on the video. While the cart is at rest, the front edge of the front wheel is at the zero of the scale. At frame 245, the string that attaches the cart to the spring is cut, releasing the cart, and it begins to roll forward. Using the distance scale, the position of the front edge of the front wheel can be tracked with time. The following table indicates the position at different frames.

What is the displacement of the cart 6 frames (in other words, 0.10 s) into the motion? Enter your answer in meters using two significant figures.

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1. A physical therapy patient contracts her biceps muscle, andexerts a horizontal force of 180 N on the spring shown in thefigure at right. Assume the forearm rotates at the elbow. a) Drawan extended force diagram of the forearm (everything from the elbowto the tip of the fingers) showing the pivot point and all of theforces acting on the forearm where they actually are applied. Youwonât know the magnitudes (or even the directions) of these forcesuntil you finish the whole problem but just draw reasonable vectorsfor now.
b) Now draw a force diagram with the forearm as a dot. c) Use thefact that the forearm is perfectly stationary at all times to findthe horizontal force that her biceps exerts on her forearm AND theforce exerted by the bone of the upper arm (shown below the biceps)on the forearm (weight = 30N). Note that muscles can only PULL inthe direction along the muscle, but that ligaments (like the onesin the elbow that connect the upper arm with the forearm) can exertforces in any direction. d) Briefly explain in complete Englishsentences (i.e., not just equations) why the bone of the upper armexerts such a large force on the forearm. e) What is the advantageof having the point where the biceps is attached to the forearm soclose to the elbow? What is the disadvantage of having it attachedso close?

2. You are trying to roll your bicycle wheel (of mass m andradius R) over a curb (of height h). To do this, you apply ahorizontal force F in the direction of desired motion. What is theminimum magnitude of the force that will successfully raise thewheel onto the curb when the force is applied (a) at the center ofthe wheel, and (b) at the top of the wheel? (c) In which case isthe magnitude of the force the least?

3. A hay bale is being dragged along a horizontal surface withconstant speed by a force F. The hay bale is 0.6 m high, 0.3m wide,and 0.9 m long (the side the force is applied to, perpendicular tothe direction of motion). The coefficient of kinetic friction is0.33. (a) Find the magnitude of the force, F. (b) Find the height,h, at which the bale will begin to tip over if the force is appliedat that height.

A Simple Atwood Machine consists of two masses m1 and m1 that are connected by a string wound over a pulley, as seen in the figure below. m2 is larger than m1. On a piece of paper, draw two free body diagrams; one for each of the masses, showing all forces acting on each mass. Then answer the following questions. (a) Based on your free body diagram, identify the forces acting on the mass m1. Select all that apply. (m1+m2)a m1g FN m1a (m1+m2)g m2a f m2g T (b) Using the direction rosette indicate the direction for each of the forces acting on m1 that you identified in part (a). If any of the forces listed below is not applicable, enter NA. m1a= m2a= m1g= m2g= (m1+m2)a= (m1+m2)g= f= T= FN= (c) Based on your free body diagram, identify the forces acting on the mass m2. Select all that apply. T (m1+m2)g m2g m1g (m1+m2)a m1a m2a f FN (d) Using the direction rosette indicate the direction for each of the forces acting on m2 that you identified in part (c). If any of the forces listed below is not applicable, enter NA. m1a= m2a= m1g= m2g= (m1+m2)a= (m1+m2)g= f= T= FN= (e) Write Newton's Second Law equation (in the form Fnet = ma) for m1 in the y-direction. Use the first answer box for the left hand side (LHS) of the equation and the second answer box for the right hand side (RHS) of the equation. It is important to use the correct signs for each of the forces. Motion in the upward direction is positive and motion in the downward direction is negative. (Use m1, g, a, and T as appropriate.) LHS = RHS = (f) Write Newton's Second Law equation (in the form Fnet = ma) for m2 in the y-direction. Use the first answer box for the left hand side (LHS) of the equation and the second answer box for the right hand side (RHS) of the equation. It is important to use the correct signs for each of the forces. Motion in the upward direction is positive and motion in the downward direction is negative.(Use m2, g, a, and T as appropriate.) LHS = RHS = (g) Use your answers from parts (e) and (f) to get an expression for the magnitude of the tension T. (Use m1, m2, and g as appropriate.) magnitude of T = (h) Use your answers from parts (e), (f), and (g) to find the magnitude of a, the acceleration of the system. (Use m1, m2, and g as appropriate.) magnitude of a = (i) In what direction will each mass accelerate. For mass m1: For mass m2: (j) Suppose m1 = 7 kg and m2 = 11 kg. What is the tension in the string? T = (k) Suppose m1 = 7 kg and m2 = 11 kg. What is the value of the acceleration? a = (l) Suppose that m2 starts from rest at a height of 5 m. Use the Kinematic Equations to determine how long it takes for m2 to hit the ground.

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