Clicker Question #1

1 Time tB, both trains have the same velocity. trains increase speed all the time. trains have the same velocity at some time before tB. on the graph, both trains have the same acceleration. The graph shows position as a function of time for two trains running on parallel tracks. Which statement is true? Clicker Question #1 A particle with zero instantaneous acceleration must have zero instantaneous velocity Clicker Question #2 A particle with zero instantaneous velocity must have zero instantaneous acceleration Clicker Question #3 A particle with zero instantaneous velocity must have zero instantaneous acceleration Clicker Question #3 of the above A particle with zero instantaneous velocity must have zero instantaneous displacement Clicker Question #4 A travels the further distance by time tB B travels the further distance by time tB trains travel the same distance by time tB is too little information to determine the relative distances travelled The graph shows velocity as a function of time for two trains starting at rest and running on parallel tracks.

2 Which of the following is true? Clicker Question #5 velocity Register Clicker From a 10 m height you throw ball A up at 5 m/s, and you throw a ball B down at 5 m/s. When the two balls hit the ground are they: at the same speed at different speeds simultaneously A never reaches the ground Clicker Question #6 For a given initial velocity, at what angle would you maximize the time of flight? A. = 0 B. = 45 C. = 60 Clicker Question #7 D. = 90 For a given initial velocity, at what angle would you maximize the range? A. = 0 C. = 60 D. = 90 Clicker Question #8 B. = 45 A battleship simultaneously fires two shells at enemy ships. If the shells follow the parabolic trajectories shown, which ship gets hit first? B. B C. both at the same time D. need more information Clicker Question #9 What is the trajectory of our projectile?

3 CQ#10 up down What is the trajectory of the monkey? CQ#11 put , constant v , constant a , constant v In the absence of gravity, where would we aim our gun? CQ#12 the monkey the monkey the monkey With gravity, where do we aim the gun? CQ#13 the monkey the monkey the monkey Which object accelerates faster? CQ#14 projectile monkey accelerate the same to know initial conditions A hammer- thrower builds up speed by spinning around as fast as possible before releasing hammer. If thrower A spins 3 times as fast as thrower B, how much more centripetal acceleration does thrower A apply? A. The same B. 3x as much C. 1/3 as much spin rate Clicker Question #15 D. 9x as much If thrower A has a hammer that is 3 times as long as thrower B s, and both spin at the same rate, how much more centripetal acceleration does thrower A have to apply? A. The same C.

4 1/3 as much D. 9x as much radius Clicker Question #16 B. 3x as much If thrower A has a hammer that is 3 times as long as thrower B s, and both spin at the same rate, how much faster is thrower A s hammer moving in space (speed)? A. The same B. 1/3 as much D. 9x as much Clicker Question #17 C. 3x as much At what angle with respect to horizontal should she release the hammer to get maximal range? A. 0 C. 45 B. 90 D. It depends on the speed of rotation Clicker Question #18 On the weight is the same, but your mass is less. weight is less, but your mass is the same. weight is more, but your mass is the same. weight is more, but your mass is less. Clicker Question #19 Acceleration can occur in a direction perpendicular of net force A. True B. False Clicker Question #20 Acceleration can occur in a direction directly opposite of net force A. True B. False can t be negative Clicker Question #21 Velocity can occur in a direction perpendicular to net force A.

5 True B. False Clicker Question #21A A bee and a train collide. What is true about this collision? A. The bee experiences the greater magnitude of force B. The train experiences the greater magnitude of force C. The bee experiences the greater magnitude of acceleration D. Both A and C are true Clicker Question #22 Consider a car at rest. We can conclude that the downward gravitational pull of Earth on the car and the upward contact force of Earth on it are equal and opposite because 1. the two forces form an interaction pair 2. the net force on the car is zero 3. neither of the above Clicker Question #23 26 If tilt angle = 0 , what happens to the friction force Ff? remains the same. becomes zero. remains the same but is balanced by the normal force. remains the same but is balanced by a second friction force. 30 Clicker Q. #24 27 If tilt angle = 0 , what happens to the friction force Ff?

6 Remains the same. becomes zero. remains the same but is balanced by the normal force. remains the same but is balanced by a second friction force. 30 Clicker Q. #24 28 In the phrase A 9,000 N automobile to what does 9,000 N refer? mass. weight. acceleration. cost. Clicker Q. #24b Clicker Question #27 A. Pushing downward on her shoulders B. Pulling upward on a rope C. No difference A father tries to slide his daughter on a sled over snow. Which is easier? to the velocity to velocity to velocity a constant velocity, there is no friction force acting A car drives on a level road at constant velocity; in which direction does friction act? N Mg Clicker Question #29A the hill. the hill. to the hill. a constant velocity, there is no friction force acting. A car drives downhill at constant velocity; in which direction does friction act? potential acceleration without friction friction force Mg Clicker Question #29 Force of static Friction equals sN sN Fapplied when Fapplied < sN normal to the surface Clicker Question #30 Clicker Question #31 What are the dimensions of the spring constant k?

7 L-1 T-2 T-2 L T2 [k] = [F]/[x] = M L T-2 / L = M T-2 k A mass is supported by a spring with spring constant k. It s equilibrium displacement is 50 cm. If I double the mass, the new equilibrium displacement is: cm cm cm cm M Clicker Question #32 35 k A mass is supported by one spring with spring constant k has an equilibrium displacement is 50 cm. If I add another spring with the same spring constant k, the new equilibrium displacement is: cm cm cm cm Mg k x @ Equilibrium F = 0 => k x + k x Mg = 0 => x = Mg/2k k x M Clicker Question #33 How does the gravitational force between two objects change if one object s mass triples? force increases by a factor of three force remains the same force decreases by a factor of three force decreases by a factor of nine Clicker Question #34 How does the gravitational force between two objects change if the distance between them triples?

8 Force increases by a factor of three force remains the same force decreases by a factor of three force decreases by a factor of nine Clicker Question #35 If you have two planets, one three times as massive as the other, how much larger is the force on that planet as compared to the lower mass one? force is bigger by a factor of three force is the same force is smaller by a factor of three force is smaller by a factor of nine Newton s 3rd law equal and opposite forces Clicker Question #36 The work done on an object can be negative A: True B: False Clicker Question #38 The kinetic energy of an object can be negative A: True B: False Clicker Question #39 CQ #40: Last time we talked about the mass-spring system. Which forces are conservative? of the spring of gravity M Mg F = k x CQ #41: What is a isolated system? A collection of objects that is sufficiently isolated from the rest of the Universe so that no energy can be transferred Fixed in place No friction Isolated CQ #42: Sam and Cathy are standing on a roof 100 m high.

9 Sam throws a ball up with an initial speed of 10 m/s. Cathy throws a ball down with an initial speed of 10 m/s. Which ball will have a greater speed when it hits the ground? ball that Sam threw ball that Cathy threw have the same final speed one hits the ground CQ #42: Ball released from rest Work done by positive? zero? negative? y Two hikers climb the same hill. The first hiker takes a steep, direct route and gets to the top in about 1 hour. The other takes a more gentle sloping route that is 4 times longer, but can walk 2 times faster and makes it to the top in 2 hours. The power expended by the first hiker is times as large as large same as large as the power expended by the second hiker. Clicker Question #43 A sports car accelerates from 0 mph to 30 mph in s. How long does it take for it to accelerate from 0 mph to 60 mph, assuming the power of the engine to be independent of velocity and ignoring friction?

10 A. 2 s B. 3 s C. s D. 6 s Clicker Question #44 A stone is launched upward into the air. In addition to the force of gravity, the stone is subject to a frictional force due to air resistance. The time the stone takes to reach the top of its flight path is than to than the time it takes to return from the top to its original position. Clicker Question #45 Which of the following forces never does work? A. Gravity B. Friction C. Tension D. Normal force E. Spring force Clicker Question #46 A bee and a train collide. Which experiences the greater magnitude of force? bee B. The train C. They experience the same force Clicker Question #47 A bee and a train collide. Which experiences the greater magnitude of acceleration? bee B. The train C. They experience the same magnitude of acceleration Clicker Question #48 Consider two carts, of masses m and 2m, at rest on an air track.