1 / 35

Forces Practice Problems Extravaganza

Forces Practice Problems Extravaganza. #1. Two opposing forces act on the 25.0 kg ball as shown. Find the ball’s acceleration. . F A. F B. F A = 40.0 N @ 180°. F B = 75.0 N @ 0°. #1 answer:. F NET = 35.0 N @ 0°, so…. a = 1.40 m /s 2 @ 0°. #2.

leontyne
Télécharger la présentation

Forces Practice Problems Extravaganza

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Forces Practice ProblemsExtravaganza Jones Physics

  2. #1 Two opposing forces act on the 25.0 kg ball as shown. Find the ball’s acceleration. FA FB FA = 40.0 N @ 180° FB = 75.0 N @ 0° Jones Physics

  3. #1 answer: FNET = 35.0 N @ 0°, so… a = 1.40 m/s2 @ 0° Jones Physics

  4. #2 Only two forces act on the 5.00 kg box, as shown. Find the acceleration of the box. FA = 300. N @ 90° FA FB = 150. N @ 0° FB Jones Physics

  5. #2 answer: FNET = 335.0 N @ 63.4°, so… a = 67.1 m/s2 @ 63.4° Jones Physics

  6. Practice Problem #3 The earth exerts a gravitational force of 29.4 N downward on a 3-kg box which is hanging at rest from a rope. (a) Draw a free-body diagram of the stationary box. Suppose an increased tension in the rope causes the box to accelerate upward. (b) Draw the free-body diagram of the box as it accelerates upward. (c) What amount of tension would cause the box to accelerate upward at 5.00 m/s2? Jones Physics

  7. #3 answers (a) FBD with equal & opposite forces (b) FBD with bigger upward force. (c) T = 44.4 N Jones Physics

  8. #4 Two boxes, 5-kg and 3-kg, are connected by a rope and pulled to the right over a frictionless surface. The pulling force is 72.0 newtons, as shown in the figure. (a) Draw a free-body diagram of each box separately. (b) What is the acceleration of each box? (c) What is the tension in the connecting rope? 72 N applied 3 kg 5 kg Jones Physics

  9. F #4 answers 3 kg 5 kg (a) (b) Both accelerate at 9.00 m/s2 @ 0° (c) T = 45.0 N 3 kg 5 kg Jones Physics

  10. FTruck on Bug = FBug on Truck (mBug )*aBug = mTruck*(aTruck)

  11. Force Paradox When I’m in my car and accelerate forward I feel like I’m being pushed backward in my seat. The acceleration is forward but the force is backward. Confounded and confused!!! And when I decelerate I feel like I’m being pushed forward out of my seat. The acceleration is backward but the force is forward. Baffled and bewildered!!! How can Newton’s 2nd Law be true? Was Newton wrong? Resolve this paradox.

  12. Force Paradox Mules are very stubborn animals. Once upon a time there was a mule that heard about Newton’s Laws. (Mules can’t read of course!) The next day, Farmer Brown came to hitch the mule to a heavy cart, which he did. But when Farmer Brown said “Giddyup!” the mule said “Ain’t gonna do it”. Further the mule said, “I’m not going to pull the cart. I’ve heard about Newton’s Laws. According to the 2nd Law it takes a net force to accelerate an object. And according to the 3rd Law, for every force there is an equal and opposite force. So no matter how hard I pull on the cart, the cart will pull back! If I pull with 10,000,000 N, the cart pulls back 10,000,000 N. I’ll never be able to move it. We’ll never get anywhere. Therefore, I refuse to even try to pull the cart.” Can you resolve this paradox and convince the mule to pull the cart? How is the mule’s argument in error?

  13. Jones Physics

  14. Physics Warm-up Problem A 2500 kg helicopter accelerates upward at 4.0 m/s2.  What lift force is exerted on the propellers by the air? Jones Physics

  15. Warm-up Problem Answer: Flift = 34,500 N @ 90° Jones Physics

  16. #5 A 125 kg astronaut exerts a force of 250. N @ 0 on her 3000 kg space capsule. (a) Find the acceleration of the capsule. (b) Find the acceleration of the astronaut. Jones Physics

  17. #5 answers (a) 0.0833 m/s2 @ 0 (b) 2.00 m/s2 @ 180 Jones Physics

  18. #6 • Classic Elevator Problem: A 70.0 kg woman stands on a scale placed in an elevator. • What does the scale read (in N) when the • elevator accelerates upward at 2.50 m/s2? • What does the scale read (in N) when the • elevator accelerates downward at 2.50 m/s2? • What is the acceleration of the elevator when • the scale reads 125 N? • What does the scale read (in N) when the • elevator rises at a constant speed of 3.0 m/s? Jones Physics

  19. #6 answers • Classic Elevator Problem: A 70.0 kg woman stands on a scale placed in an elevator. Jones Physics

  20. Problem #7 • Three boxes are accelerated across a frictionless surface by a rope applying 12.0 N. • Determine the acceleration of the boxes. • Determine the tension in the rope between the • 2-kg and 3-kg boxes. • Determine the tension in the rope between the • 3-kg and 1-kg boxes. 1kg 12 N applied 3 kg 2 kg Jones Physics

  21. #7 answers • a = • T2-3 = • T1-3 = 1kg 12 N applied 3 kg 2 kg Jones Physics

  22. #8 • A 2.00 kg box is kicked and begins to slide horizontally across a rough surface with initial velocity of 12.0 m/s @ 0°. The force of sliding friction is a constant 15.0 N. • Draw a FBD of the box as it skids (decelerates)? • What is the acceleration of the box? • What distance does the box slide during the skid? Jones AP Physics

  23. #8 answers • A 2.00 kg box is kicked and begins to slide horizontally across a rough surface with initial velocity of 12.0 m/s @ 0°. The force of sliding friction is a constant 15.0 N. • FBD • a = • d = Jones AP Physics

  24. #9 A 10.0 kg block is placed on a frictionless ramp as shown. Find the block’s acceleration. 10 kg  = 40 Jones Physics

  25. #9 answer a = 6.3 m/s2 @ 220° 10 kg  = 40 Jones Physics

  26. Problem #10 • The total mass of everything hanging from an elevator’s support cable (including passengers) is 1500 kg. • What is the tension in the cable when the elevator is at rest? • What is the tension in the cable when the elevator descends at a constant 4.0 m/s? • What is the tension in the cable when the elevator accelerates downward at 2.5 m/s2? • What is the acceleration of the elevator when the cable tension is 18 kN? Jones Physics

  27. #10 answers • 14,700 N • 14,700 N • 10,950 N • 2.20 m/s2 @ 90° Jones Physics

  28. #11 A 1300-kg train car is pulled up a hill at a constant velocity by a cable as shown. Assuming no friction, what tension is in the cable? 1300 kg 20 Jones Physics

  29. #11 answer T = 4360 N 1300 kg 20 Jones Physics

  30. #12 • Two boxes are accelerated across a frictionless surface by a rope applying 24.0 N to the bottom box. The top box does not slip. • Determine the acceleration of the boxes. • Determine all the normal forces acting on each box. • Determine the force of static friction on the top box. 2 kg 24 N applied 6 kg Jones Physics

  31. #13 • A 5.00 kg block is sliding 8.00 m/s at the bottom of a 30 ramp. As the box slides up the ramp, it decelerates due to gravity and friction. The force of kinetic friction has a constant magnitude of 12.7 N. • Draw the F.B.D. of the block and determine all the forces on the block: Fg, FN, & Ff (magnitude & direction). • Calculate the block’s acceleration. • Calculate the sliding distance along the ramp. 5 kg Θ = 30 Jones Physics

  32. #14 A 25.0-Newton sign hangs from two chains as shown below. Determine the tension in each of the chains. TA = ____ TB = ____ A B 60 30 HONORS PHYSICS DUE DATES 25.0 N Jones AP Physics

  33. #15 • Two blocks are connected by a massless string which passes over a frictionless pulley as shown below. Determine the tension in the string and the acceleration of the boxes if • the horizontal surface is frictionless. • the coefficient of kinetic friction between the 3.00 kg • block and the horizontal surface is 0.250. 3 kg 2 kg Jones Physics

  34. #16 ACME PULLEY The Atwood Machine: Assuming the two masses shown are connected by a massless string over a frictionless pulley, determine the acceleration of the boxes and the tension in the string. Frictionless! 7 kg 3 kg Jones Physics

  35. Quick Quiz #1 A junkyard crane lifts and lowers a smashed car. Suppose the mass of the car is 2000 kg, and the mass of the cable is negligible. (a) Draw a F.B.D. of the car, and calculate its weight, Fg. Find the tension in the cable when the car: (b) accelerates 2.00 m/s2 @ 90.0, (c) accelerates 1.00 m/s2 @ 270.0, and (d) rises at a constant 2.00 m/s @ 90.0. Jones Physics

More Related