A hockey puck slides on ice at constant velocity. What is the net force acting on the puck?

Transcription

1 A hockey puck slides on ice at constant velocity. What is the net force acting on the puck? A. Something more than its weight B. Equal to its weight C. Something less than its weight but more than zero D. It depends on the speed of the puck E. Zero

2 You kick a smooth flat stone out on a frozen pond. The stone slides, slows down and eventually stops. You conclude that: A. the force pushing the stone forward finally stopped pushing on it B. no net force acted on the stone C. a net force acted on it all along D. the stone simply ran out of steam E. the stone has a natural tendency to be at rest

3 You push a heavy crate across the floor at a constant velocity. What is the net force acting on the crate? A. Something more than its weight B. Equal to its weight C. Something less than its weight but more than zero D. It depends on the speed of the crate E. Zero

4 An elevator is moving up at a steady speed. v 1) Identify all forces acting on the elevator and draw a free body diagram. (Neglect any friction between the elevator and the shaft.) 2) Which is greater, the cable tension or the weight of the elevator?

5 A box is pushed across a rough table at constant speed. v 1) Identify all forces acting on the box and draw a free body diagram. 2) Which is greater, the pushing force or the friction force?

6 A box is pushed across a rough table and released. v 0 1) At the instant it is released (i.e., just after), identify all forces acting on the box and draw a free body diagram. 2) In what direction is the net force on the box?

7 A small car collides with a large truck. Which experiences the greater impact force? A. The car B. The truck C. Both the same D. It depends on the velocity of each E. It depends on the mass of each

8 A small car collides with a large truck. Which experiences the greater acceleration? A. The car B. The truck C. Both the same D. It depends on the velocity of each E. It depends on the mass of each

9 When you climb up a rope, the first thing you do is pull down on the rope. How do you manage to go up the rope by doing that?? A. This slows your initial velocity which is already upward B. You don t go up, you re too heavy C. You re not really pulling down it just seems that way D. The rope actually pulls you up E. You are pulling the ceiling down

10 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 A. the two forces form an interaction pair. B. the net force on the car is zero. C. neither of the above

11 You tie a rope to a tree and you pull on the rope with a force of 100 N. What is the tension in the rope? A. 0 N B. 50 N C. 100 N D. 150 N E. 200 N

12 Two tug-of-war opponents each pull with a force of 100 N on opposite ends of a rope. What is the tension in the rope? A. 0 N B. 50 N C. 100 N D. 150 N E. 200 N

13 From rest, we step on the gas of our Ferrari, providing a constant force F for 4 s, speeding it up to a final speed v. If the applied force were only 1/2 F, how long would it have to be applied to reach the same final speed? A. 16 s B. 8 s C. 4 s D. 2 s E. 1 s v F

14 Consider a person standing in an elevator that is accelerating upward. The upward normal force N exerted by the elevator floor on the person is A. larger than B. identical to C. smaller than the downward weight W of the person.

15 An object is being lowered by a string, and its speed is decreasing. How do the weight of the object and the tension in the string compare? A. T > mg B. T < mg C. T = mg D. Can t tell without more information.

16 A car rounds a curve while maintaining constant speed. Is there a net force on the car as it rounds the curve? A. No B. Yes C. It depends on the sharpness of the curve and/or the speed of the car.

17 A constant force is exerted on a cart that is initially at rest on an air track. Friction between the cart and the track is negligible. The force acts for a short time interval and gives the cart a certain final speed. To reach the same final speed with a force that is only half as big, the force must be exerted on the cart for a time interval A. four times as long as B. twice as long as C. equal to D. half as long as E. a quarter of that for the stronger force.

18 A constant force is exerted for a short time interval on a cart that is initially at rest on an air track. This force gives the cart a certain final speed. The same force is exerted for the same length of time on another cart, also initially at rest, that has twice the mass of the first one. The final speed of the heavier cart is A. one-fourth B. four times C. half D. double E. the same as that of the lighter cart.

19 A constant force is exerted for a short time interval on a cart that is initially at rest on an air track. This force gives the cart a certain final speed. Suppose we repeat the experiment but, instead of starting from rest, the cart is already moving with constant speed in the direction of the force at the moment we begin to apply the force. After we exert the same constant force for the same short time interval, the increase in the cart s speed A. is equal to two times its initial speed. B. is equal to the square of its initial speed. C. is equal to four times its initial speed. D. is the same as when it started from rest. E. cannot be determined from the information provided.