# Application of Newtons laws: free body diagram Physics 7C lecture 03 Thursday O

## Application of Newtons laws: free body diagram Physics 7C lecture 03 Thursday O

Jacobs, Jim, Morning Show Producer/Host has reference to this Academic Journal, PHwiki organized this Journal Application of Newtons laws: free body diagram Physics 7C lecture 03 Thursday October 3, 8:00 AM  9:20 AM Engineering Hall 1200 Newtons laws Newtons First Law of Motion: when as long as ces are balanced the object will keep its motion/velocity. Newtons Second Law of Motion: F = m a, as long as ce causes changes to the motion/velocity. Newtons Third Law of Motion: action-reaction pairs Yet: The laws are simple to state but intricate in their application. Lets do some iClicker questions first. Q4.1 v Motor Cable Elevator An elevator is being lifted at a constant speed by a steel cable attached to an electric motor. There is no air resistance, nor is there any friction between the elevator in addition to the walls of the elevator shaft. The upward as long as ce exerted on the elevator by the cable is A. greater than the downward as long as ce of gravity. B. equal to the as long as ce of gravity. C. less than the as long as ce of gravity. D. any of the above, depending on the speed of the elevator.

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A4.1 v Motor Cable Elevator An elevator is being lifted at a constant speed by a steel cable attached to an electric motor. There is no air resistance, nor is there any friction between the elevator in addition to the walls of the elevator shaft. The upward as long as ce exerted on the elevator by the cable is A. greater than the downward as long as ce of gravity. B. equal to the as long as ce of gravity. C. less than the as long as ce of gravity. D. any of the above, depending on the speed of the elevator. Q4.2 v Motor Cable Elevator An elevator is being lowered at a constant speed by a steel cable attached to an electric motor. There is no air resistance, nor is there any friction between the elevator in addition to the walls of the elevator shaft. The upward as long as ce exerted on the elevator by the cable is A. greater than the downward as long as ce of gravity. B. equal to the as long as ce of gravity. C. less than the as long as ce of gravity. D. any of the above, depending on the speed of the elevator. A4.2 v Motor Cable Elevator An elevator is being lowered at a constant speed by a steel cable attached to an electric motor. There is no air resistance, nor is there any friction between the elevator in addition to the walls of the elevator shaft. The upward as long as ce exerted on the elevator by the cable is A. greater than the downward as long as ce of gravity. B. equal to the as long as ce of gravity. C. less than the as long as ce of gravity. D. any of the above, depending on the speed of the elevator.

Q4.5 A. crate A exerts more as long as ce on crate B than B exerts on A B. crate A exerts less as long as ce on crate B than B exerts on A C. crate A exerts as much as long as ce on crate B as B exerts on A D. Answer depends on the details of the friction as long as ce If the two crates are accelerating to the right, A B F A lightweight crate (A) in addition to a heavy crate (B) are side-by-side on a horizontal floor. You apply a horizontal as long as ce F to crate A. There is friction between the crates in addition to the floor. A4.5 A. crate A exerts more as long as ce on crate B than B exerts on A B. crate A exerts less as long as ce on crate B than B exerts on A C. crate A exerts as much as long as ce on crate B as B exerts on A D. Answer depends on the details of the friction as long as ce If the two crates are accelerating to the right, A B F A lightweight crate (A) in addition to a heavy crate (B) are side-by-side on a horizontal floor. You apply a horizontal as long as ce F to crate A. There is friction between the crates in addition to the floor. Q4.6 v Motor Cable Elevator An elevator is being lowered at constant speed by a steel cable attached to an electric motor. There is no air resistance, nor is there any friction between the elevator in addition to the walls of the elevator shaft. The upward as long as ce exerted on the elevator by the cable has the same magnitude as the as long as ce of gravity on the elevator, but points in the opposite direction. Why A. Newtons first law B. Newtons second law C. Newtons third law

A4.6 v Motor Cable Elevator An elevator is being lowered at constant speed by a steel cable attached to an electric motor. There is no air resistance, nor is there any friction between the elevator in addition to the walls of the elevator shaft. The upward as long as ce exerted on the elevator by the cable has the same magnitude as the as long as ce of gravity on the elevator, but points in the opposite direction. Why A. Newtons first law B. Newtons second law C. Newtons third law Q4.3 The graph to the right shows the velocity of an object as a function of time. Which of the graphs below best shows the net as long as ce versus time as long as this object A. B. C. D. E. A4.3 The graph to the right shows the velocity of an object as a function of time. Which of the graphs below best shows the net as long as ce versus time as long as this object A. B. C. D. E.

Free-body diagrams A free-body diagram is a sketch showing all the as long as ces acting on an object. Why do we need it What is the tension as long as ce in the rope Free-body diagrams We need to isolate the objects in addition to study the as long as ces on each of them. T1 W1 T1 W2 T2 T2 W3 Note: W = m g action-reaction pairs Free-body diagrams We can apply the 2nd law to each of the following, or to the group. T1 W1 T1 W2 T2 T2 W3 The three objects share the same acceleration: a = (F-W1-W2-W3) / (m1+m2+m3) = F/(m1+m2+m3)  g = 200/(6+4+5)  9.8 = 3.53 m/s2

Free-body diagrams Now we focus on m1 in addition to solve as long as tension T1. T1 W1 as long as the upper mass, apply the 2nd law: F-W1-T1 = m1 a we have: T1 = F-W1-m1 a = 200-69.8-63.53 = 120.02 N Free-body diagrams Similarly we focus on the rope in addition to solve as long as tension T2. T1 W2 T2 T1-W2-T2 = m2 a we have: T2 = T1-W2-m2 a = 120.02-49.8-43.53 = 66.7 N Free-body diagrams We can double check the result on the lower mass: T2 W3 T2-W3 = m3 a we have calculated: T2 = 66.7 N a = 3.53 m/s2 66.7  59.8 = 5 3.53 true!

Free-body diagramsexamples A free-body diagram is a sketch showing all the as long as ces acting on an object. Free-body diagramsexamples A free-body diagram is a sketch showing all the as long as ces acting on an object. Free-body diagramsexamples

Q4.9 A person pulls horizontally on block B, causing both blocks to move horizontally as a unit. There is friction between block B in addition to the horizontal table. If the two blocks are moving to the right at constant velocity, A. the horizontal as long as ce that B exerts on A points to the left. B. the horizontal as long as ce that B exerts on A points to the right. C. B exerts no horizontal as long as ce on A. D. not enough in as long as mation given to decide A4.9 A person pulls horizontally on block B, causing both blocks to move horizontally as a unit. There is friction between block B in addition to the horizontal table. If the two blocks are moving to the right at constant velocity, A. the horizontal as long as ce that B exerts on A points to the left. B. the horizontal as long as ce that B exerts on A points to the right. C. B exerts no horizontal as long as ce on A. D. not enough in as long as mation given to decide A woman pulls on a 6.00-kg crate, which in turn is connected to a 4.00-kg crate by a light rope. The light rope remains taut. A. is subjected to the same net as long as ce in addition to has the same acceleration. B. is subjected to a smaller net as long as ce in addition to has the same acceleration. C. is subjected to the same net as long as ce in addition to has a smaller acceleration. D. is subjected to a smaller net as long as ce in addition to has a smaller acceleration. E. none of the above Q4.12 Compared to the 6.00-kg crate, the lighter 4.00-kg crate

A woman pulls on a 6.00-kg crate, which in turn is connected to a 4.00-kg crate by a light rope. The light rope remains taut. A. is subjected to the same net as long as ce in addition to has the same acceleration. B. is subjected to a smaller net as long as ce in addition to has the same acceleration. C. is subjected to the same net as long as ce in addition to has a smaller acceleration. D. is subjected to a smaller net as long as ce in addition to has a smaller acceleration. E. none of the above A4.12 Compared to the 6.00-kg crate, the lighter 4.00-kg crate A car engine is suspended from a chain linked at O to two other chains. Which of the following as long as ces should be included in the free-body diagram as long as the engine A. tension T1 B. tension T2 C. tension T3 D. two of the above E. T1, T2, in addition to T3 Q5.1 A car engine is suspended from a chain linked at O to two other chains. Which of the following as long as ces should be included in the free-body diagram as long as the engine A. tension T1 B. tension T2 C. tension T3 D. two of the above E. T1, T2, in addition to T3 A5.1

Two-dimensional equilibrium A car engine hangs from several chains. Two-dimensional equilibrium A car engine hangs from several chains. Q5.3 When released, the cart accelerates up the ramp. Which of the following is a correct free-body diagram as long as the cart A. B. C. D. m1a m1a w1 w1 w1 w1 T T T T n n n n A cart (weight w1) is attached by a lightweight cable to a bucket (weight w2) as shown. The ramp is frictionless.

Bodies connected by a cable in addition to pulley If the cart is moving at constant speed, what is w2/w1 Bodies connected by a cable in addition to pulley If the cart is moving at constant speed, what is w2/w1 consider the bucket T = w2 Bodies connected by a cable in addition to pulley If the cart is moving at constant speed, what is w2/w1 consider the cart along x direction: W1 Sin 15o  T = 0 Thus: W2 = W1 Sin 15o in addition to : W2/W1 = Sin 15o = 0.26

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