Midterm 1 Review Chapters 1-5 © 2015 Pearson Education, Inc.

General Strategies Text: p. 55 © 2015 Pearson Education, Inc.

General Strategies for Motion Problems Text: p. 55 © 2015 Pearson Education, Inc.

Constant Acceleration Equations For motion with constant acceleration: Velocity changes steadily: The position changes as the square of the time interval: We can also express the change in velocity in terms of distance, not time: Text: p. 43 © 2015 Pearson Education, Inc.

Example Problem Passengers on the Giant Drop, a free-fall ride at Six Flags Great America, sit in cars that are raised to the top of a tower. The cars are then released for 2.6 s of free fall, after which the brakes clamp and they come to rest in a time of 1.0 s. What is the minimum possible height of the tower? Answer: Neglecting any air resistance or other friction the car would be moving 2.6  9.8 = 25 m/s. To decelerate to zero from this speed in 1 s the acceleration is a = 25m/s/1s = 25 m/s2 and the acceleration is upward. To calculate the height, break the motion into the two phases defined by the two values of acceleration. In the first phase the distance = ½  9.8  2.62 = 33 m. In the second phase the distance = ½  25  12 = 12.5 m. The total distance is thus 46 m. © 2015 Pearson Education, Inc.

Summary: General Principles Text: p. 89 © 2015 Pearson Education, Inc.

Example Problem The longest recorded pass in an NFL game traveled 83 yards horizontal distance. Assuming the pass was thrown from an optimal 45˚ (to the horizontal) angle, and that the ball left the QB’s hand 2.0 yards above the ground, and was caught by a diving pass at ground level, how long was the ball in the air, and what was the ball’s speed in mph? Answer: © 2015 Pearson Education, Inc.

Summary: Applications Text: p. 89 © 2015 Pearson Education, Inc.

Example Problem A kayaker needs to paddle north across a 100. m wide harbor. The tide is going out, creating a tidal current flowing east at 2.0 m/s. The kayaker can paddle with a speed of 3.0 m/s. In what direction should he paddle in order to travel straight north across the harbor? How long will it take him? Answer: © 2015 Pearson Education, Inc.

Summary: Applications Text: p. 118 © 2015 Pearson Education, Inc.

Summary: General Strategy Text: p. 152 © 2015 Pearson Education, Inc.

Catalog of Forces Revisited © 2015 Pearson Education, Inc. Text: p. 144

Example Problem A car traveling at 20 m/s stops in a distance of 50. m. Assume that the deceleration is constant. The coefficients of friction between a passenger and the seat are µs = 0.50 and µk = 0.30. Will a 70-kg passenger slide off the seat if not wearing a seat belt? Answer: Using the kinematic values provided, the deceleration is 4 m/s2. The maximum force that can be provided by the seat on the person from static friction (to prevent the person from sliding) is s times the normal force which in this case is s times the weight. s  g = .5  9.8 = 4.9 m/s2, thus static friction is strong enough to prevent slippage at a deceleration up to 4.9 m/s2. Since the deceleration of the car is only 4, the person does not slip. The mass of the person and the coefficient of kinetic friction are not needed. © 2015 Pearson Education, Inc.

QuickCheck 2.7 Which velocity-versus-time graph goes with this position graph? Answer: C © 2015 Pearson Education, Inc. 14

QuickCheck 2.7 Which velocity-versus-time graph goes with this position graph? C. © 2015 Pearson Education, Inc. 15

QuickCheck 2.22 Here is a motion diagram of a car speeding up on a straight road: The sign of the acceleration ax is Positive. Negative. Zero. Answer: B © 2015 Pearson Education, Inc.

QuickCheck 2.22 Here is a motion diagram of a car speeding up on a straight road: The sign of the acceleration ax is Positive. Negative. Zero. Speeding up means vx and ax have the same sign. © 2015 Pearson Education, Inc.

QuickCheck 3.6 The diagram shows three points of a motion diagram. The particle changes direction with no change of speed. What is the acceleration at point 2? Answer: B © 2015 Pearson Education, Inc. 18

QuickCheck 3.6 The diagram shows three points of a motion diagram. The particle changes direction with no change of speed. What is the acceleration at point 2? Acceleration of changing direction B. © 2015 Pearson Education, Inc. 19

QuickCheck 3.14 A ball rolls up the ramp, then back down. Which is the correct acceleration graph? D. © 2015 Pearson Education, Inc.

QuickCheck 3.14 A ball rolls up the ramp, then back down. Which is the correct acceleration graph? D. © 2015 Pearson Education, Inc.

QuickCheck 3.18 Projectiles 1 and 2 are launched over level ground with the same speed but at different angles. Which hits the ground first? Ignore air resistance. Projectile 1 hits first. Projectile 2 hits first. They hit at the same time. There’s not enough information to tell. Answer: B © 2015 Pearson Education, Inc.

QuickCheck 3.18 Projectiles 1 and 2 are launched over level ground with the same speed but at different angles. Which hits the ground first? Ignore air resistance. Projectile 1 hits first. Projectile 2 hits first. They hit at the same time. There’s not enough information to tell. © 2015 Pearson Education, Inc.

QuickCheck 4.16 10-year-old Sarah stands on a skateboard. Her older brother Jack starts pushing her backward and she starts speeding up. The magnitude of the force of Jack on Sarah is Greater than the magnitude of the force of Sarah on Jack. Equal to the magnitude of the force of Sarah on Jack. Less than the magnitude of the force of Sarah on Jack. Answer: B © 2015 Pearson Education, Inc.

QuickCheck 4.16 10-year-old Sarah stands on a skateboard. Her older brother Jack starts pushing her backward and she starts speeding up. The force of Jack on Sarah is Greater than the magnitude of the force of Sarah on Jack. Equal to the magnitude of the force of Sarah on Jack. Less than the magnitude of the force of Sarah on Jack. © 2015 Pearson Education, Inc.

QuickCheck A 100-kg block with a weight of 980 N hangs on a rope. Compare the tension in the rope if the block is stationary vs. if the block is moving upward at a steady speed of 5 m/s. The tension is greater when the block is stationary. The tension is greater when the block is moving. The tension is the same in both cases. Not enough information to tell. Answer: E © 2015 Pearson Education, Inc.

QuickCheck A 100-kg block with a weight of 980 N hangs on a rope. Compare the tension in the rope if the block is stationary vs. if the block is moving upward at a steady speed of 5 m/s. The tension is greater when the block is stationary. The tension is greater when the block is moving. The tension is the same in both cases. Not enough information to tell. Answer: E © 2015 Pearson Education, Inc.

QuickCheck 5.2 The box is sitting on the floor of an elevator. The elevator is accelerating upward. The magnitude n of the normal force on the box is (w is the weight) n > w n = w n < w n = 0 Not enough information to tell Answer: A © 2015 Pearson Education, Inc. 28

QuickCheck 5.2 The box is sitting on the floor of an elevator. The elevator is accelerating upward. The magnitude n of the normal force on the box is (w is the weight) n > w n = w n < w n = 0 Not enough information to tell Upward acceleration requires a net upward force. © 2015 Pearson Education, Inc. 29

QuickCheck 5.3 A box is being pulled to the right at steady speed by a rope that angles upward. In this situation: n > mg n = mg n < mg n = 0 Not enough information to judge the size of the normal force Answer: C © 2015 Pearson Education, Inc. 30

QuickCheck 5.3 A box is being pulled to the right at steady speed by a rope that angles upward. In this situation: n > mg n = mg n < mg n = 0 Not enough information to judge the size of the normal force © 2015 Pearson Education, Inc. 31

QuickCheck 5.9 A box is being pulled to the right over a rough surface. T > fk, so the box is speeding up. Suddenly the rope breaks. What happens? The box Stops immediately. Continues with the speed it had when the rope broke. Continues speeding up for a short while, then slows and stops. Keeps its speed for a short while, then slows and stops. Slows steadily until it stops. Answer: E © 2015 Pearson Education, Inc. 32

QuickCheck 5.9 A box is being pulled to the right over a rough surface. T > fk, so the box is speeding up. Suddenly the rope breaks. What happens? The box Stops immediately. Continues with the speed it had when the rope broke. Continues speeding up for a short while, then slows and stops. Keeps its speed for a short while, then slows and stops. Slows steadily until it stops. © 2015 Pearson Education, Inc. 33