unit+3+Forces+2015


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Answers: 1a) 6.93 m/s2 1b) no 2a) 37.6 degrees 2b) 4.6 m/s2 3a) 2.25 s 3b) 8.87 m/s 3c) 0.0175



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Tension notes and sample problem (from whiteboard)

Tuesday





=Practice Test On Newton's Laws=

1) What are Newton's Laws? (all 3 in the correct order)

2) Use the concept of inertia to explain how concussions happen.

3) If a bug splats on the window of a moving car, both the car and the bug experience the same force. Why does the bug splat but the car seem unaffected. Is the car completely unaffected? What will happen to the car's acceleration at the moment of impact?

4) Imagine a little boy pulling on a wagon. If Newton's 3rd Law is true and the wagon pulls back on the boy with the same force the boy pulls on the wagon, how is it possible for the boy to pull the wagon across the yard? (what other forces are involved other than just the boy pulling on the wagon?)

5) What are "force pairs" and give an example. (3rd Law)

6) How much force does it take to accelerate a 0.08 kg. hockey puck at 120 m/s2?

7) If two people are pulling on a wagon in different directions at angles of 30 degrees and 50 degrees. How much harder does the person pulling at 50 degrees have to pull to keep the wagon from moving? (Give a percentage compared to the 30 degree person)

8) A 15 kg. box sits on a frictionless surface. If a 40 N force pushes the box up and to the right at an angle of 25 degrees above horizontal while another 30 N force pushes the box down and to the right at an angle of 70 degrees below horizontal, what will be the net force on the box, the direction it will it will move (include angle), and its acceleration?

9) A car engine provides enough force to speed a 1200 kg. car from 0 m/s to 40 m/s within a distance of 500 meters. What force was provided by the engine?

10) Two identical boxes are placed on identical ramps with the same angle. One of the boxes has extra weights placed in it. Which box will slide down the ramp with the highest acceleration? Why?

11) A 4 kg. box is placed on a 20 meter long frictionless ramp of 33 degrees. What is the box's acceleration down the ramp? How long will it take to travel the full distance?

12) Imagine the same situation as problem #11 and assume the coefficient of kinetic friction between the box and the ramp is 0.34. What is the box's acceleration now and how long will it take to move down the ramp?

13) Prove that the tangent of the angle at which an object begins to slip down an inclined plane is equal to the coefficient of static friction between the two surfaces.

14) Two ropes attached to the ceiling are holding up a 30 kg. safe. One rope is making a 30 degree angle with the ceiling while the other rope is making a 60 degree angle with the ceiling. What is the tension in both ropes?



NOTE: The answer for #7 should be F1 = 135% of F2 or F2 = 74% of F1