Extra Credit Final Practice

Transcription

1 Velocity (m/s) Elements of Physics I Spring 218 Extra Credit Final Practice 1. Use the figure to answer the following questions. Which of the lines indicate a) Constant velocity b) Constant acceleration c) Varying acceleration d) A displacement of e) A curved position vs time graph f) A linear position vs time graph g) A horizontal line on an acceleration vs time graph C A D B Use curve A of the figure above to Time (s) answer the following questions. a) Calculate the acceleration at 5s b) At which time is the force acting in the opposite direction of velocity, 2s or 8s, or neither? c) If the mass of the object creating curve A is 4kg, calculate the net force acting on it d) Sketch a FBD of the object at 2s indicating all forces acting. Indicate also the direction of velocity and acceleration at that time. e) Describe in detail the motion of the object for the given 1s. 3. Use curve D of the figure above to answer the following questions. a) Sketch the position vs time graph for 1s. Assume an initial position of. b) Calculate the velocity and acceleration at 6s c) Calculate the net force acting on the object d) What is the objects displacement in 1s? 4. A 1kg object sliding across a horizontal surface is acted upon by the force shown. Calculate the following a) The horizontal and vertical components of the vector b) The horizontal acceleration of the block c) The displacement of the block in 5s, given that initial velocity was 1m/s 3 N d) The work done by the 3N force in 5s e) The change in KE of the block 2 f) The normal force 5. A 3kg block slides eastward across the floor, decreasing its velocity by 4m/s every second a) Draw the FBD for the block showing forces that must be acting. Indicate direction of velocity. b) Calculate the blocks acceleration. Indicate its direction near the FBD. c) Calculate the net force acting on the block. d) I would expect to see a linear or curved position vs time graph?

2 Position (ft) 6. In a perfect world, we try our centripetal force experiment. We twirl a mass, M=.5kg, in a horizontal circle over our head. A string connects our twirling mass to our hanging mass, m. The time for 1 revolutions is measured to be 7.4s and the radius, R, is.65m. a) Calculate the velocity of the twirling mass b) Calculate the acceleration of the twirling mass c) Calculate the Tension in the string. d) Calculate the mass, m of the hanging mass. e) The figure right shows the twirling mass from the top. If the string were to suddenly break at the moment shown, in which direction would the mass, M, fly off? m R a Twirling mass b M c 7. A student walks back and forth in front of a motion detector. Assume at 2s, the student is walking away from the motion detector. a) Calculate the student s displacement for the 18s. b) Indicate a range of time where velocity is fairly constant c) Describe the motion of the student from 2 to 6s d) Calculate the average velocity from 14s to 18s time (s) 8. A 2lb gorilla jumps out of an airplane. Thankfully he has a parachute and quickly reaches a terminal velocity of 3ft/s!! a) Calculate the net force acting on the gorilla while falling at a constant 3ft/s. b) At this moment, calculate the force due to air resistance or drag acting on gorilla + parachute. 9. On a planet where gravity is 3m/s 2, you kick a 2kg ball at an angle of 55 above the horizontal with a velocity of 2m/s. Calculate the following a) The acceleration of the ball at 1.5 s b) The total mechanical energy at the maximum height c) The maximum height reached d) The total mechanical energy just before impact, assuming the ball lands from the same height from which it was kicked. e) The velocity just prior to impact 1. On a world made of frictionless ice, 4kg me + 2kg physics book is sliding across the floor at 3 m/s. I suddenly realize I m heading towards a wall!! Quickly, I unload my physics book, throwing it towards the wall at 5m/s. Will I miss the wall? Calculate my final velocity. And if I m going to hit the wall, calculate my change in momentum, impulse and force felt if I come to a stop in.4s.

3 11. On a world where gravity is only 6m/s 2, Donald duck, of mass 2kg, stands on a scale in an elevator. What does the scale read when the elevator is a) Stationary b) Moving upward at a constant 1m/s c) Accelerating upward at 6m/s 2 d) Draw all the forces acting on Donald scale 12. A 4kg ball is dropped from a height of 2m. a) Calculate the velocity just prior to impact. b) Calculate the time taken to fall 2m c) Calculate the total mechanical energy when at 1m 13. You swat a fly with your hand, hitting the fly. a) Which experiences the greater impulse, your hand or the fly? b) If in contact for.2s, which experiences the greater force, your hand or the fly? c) Which experiences the greater acceleration and why? 14. Due to an odd mishap, your.2kg cell phone finds itself in a stable orbit 1km above the surface of Mercury. a) What is the magnitude and direction of the acceleration of your cell phone as it orbits Mercury? b) Calculate the force that attracts your cell phone to Mercury (same as the force which attracts Mercury to your cell phone) c) With what velocity must your cell phone be moving to maintain its orbit around Mercury? d) Calculate time of orbit in minutes. e) If I notice my cell phone beginning to orbit a bit lower, will its forward velocity have increased or decreased? 15. A 2kg rock is kicked, giving it an impulse of 45Ns. The rock then careens off a cliff as shown. a) Assuming the velocity of the rock prior to receiving the impulse is, with what velocity does it go careening off the cliff? b) If the rock is in the air for 8s, how far away from the cliff does the rock land? c) Calculate the height of the cliff V 16. Consider the following cases regarding a.7kg ball. (i) A ball hits the floor with a velocity of 6m/s and comes to a stop in.1s (ii) A ball hits the floor with a velocity of 6m/s and comes to a stop in.5s (iii) A ball hits the floor with a velocity of 6m/s, remains in contact with the floor for.1s, and rebounds at 4m/s. a) Order the events largest impulse to smallest. If any have the same impulse, say so. b) Order the events largest change in momentum to smallest. If any have the same momentum change, say so. c) Order the events, largest force to smallest. If any have the same force, say so.

4 Position (m) Answers 1. a) D b) A, B c) C d) A e) A, B, C f) D g) A, B 2. a) 1.6m/s 2 b) 2s c) 6.4N d) e) Object slows down, then at 5s it pauses, reverses direction, then speeds up in the opposite direction. 3. a) 8 b) v = 8m/s a = c) F = d) Δx = 8m F, a V 5 1 time (s) 4. a) F x = 28.2N, F y = 1.3N b) a = 2.82m/s 2 c) Δx = 85.3m d) 244J e) ΔKE = 244J f) = 87.7N V F, a 5. a) b) a = -4m/s 2 c) F = -12N d) curved 6. a) v = 5.5m/s b) a = 46.9m/s 2 c) T = 23.4N d) m = 2.4kg e) b 7. a) Δx = 3ft b) multiple answers. 13s-18s is good. c) walking away, pause at 4s, reverse direction, walk towards. d) v = 7.5ft/s 8. a) F = b) F drag = 2lb 9. a) g = 3m/s 2 b) ME = 4J c) Δy = 44.7m d) ME = 4J e) V = 2m/s at I will hit the wall at 2m/s. I = Δmv = -8kgm/s F = -2N 11. a) = 12N b) 12N c) = 24N d) 12. a) v = 19.8m/s b) t = 2s c) ME = 784J 13. a) Same b) same c) fly experiences most acceleration due to less mass 14. a) g = 3.41m/s 2 towards Mercury b) F =.7N towards Mercury c) v = 2942m/s d) T = 9min, 22sec e) decreased

5 15. a) v = 225m/s b) Δx = 18m c) Δy = 313.6m 16. a) (iii), then (i) and (ii) are the same b) (iii), then (i) and (ii) are the same c) (iii), (i), (ii)