PHYS 1401 – General Physics I

Homework #2

Ch.3

1. For the vectors A and B shown below, graphically find the following. a) A + B

b) B – A c) 2A – 3B

2. A girl walks 2.4 miles in a direction of 35° N of E and then 3.5 miles in a direction of 28° S of E. a) Make a sketch showing the vector addition and indicate the vector showing the net displacement. b) Explain how you can use components to add the vectors. c) Give the magnitude and direction of the net displacement. Use components to perform the vector addition.

3. A ball is tossed horizontally. a) Sketch the trajectory of the ball, and at 5 different locations on the trajectory b) indicate the acceleration of the ball.

4. A football is kicked from ground level towards a goal post located 30.0 m away so that on the way down it just clears the goal post. The x-component of the initial velocity is 12 m/s and the post is 3.0 m high. a) Sketch the situation and indicate the trajectory of the ball on your sketch. b) Draw a vector diagram for the ball at the final position.

c) Find the time that it takes the ball to reach the goal post, the y-component of the initial velocity, and the angle at which the ball was kicked?

5. A kayaker is paddling in a river that heads due south and has a current of 2.5 mi/hr. The kayaker paddles at 4.5 mi/hr, in the reference frame of the river, at an angle of 42° S of W. a) Sketch the situation. b) Describe the relationship between the reference frame of the kayaker and an observer standing on shore. c) Find the velocity as seen by the observer on shore. (Remember, velocity is a vector so you need both magnitude and direction.)

6. A person standing on a sidewalk sees rain falling straight down. a) Describe how the rain appears to a person driving down the street. b) Explain, using reference frames, why it appears this way to the driver. Include a diagram in your explanation.

Ch. 4

7. You and two friends see a box sitting at rest on a table. Your first friend tells you because the box is at rest, no forces act on the box. Your second friend tells you that the table cancels out the gravity and that this is why the box is at rest. Is either of your friends correct? Settle the dispute for your friends.

8. The same force is applied to the six boxes shown. a) Rank the acceleration of the boxes from least to most. b) Carefully explain your reasoning.

9. A coin is tossed into the air. Describe the force(s) acting on the coin a) on the way up, b) at the top of the motion and c) on the way down. Explain your reasoning for each.

10. A 4500 kg truck collides with a 1500 kg compact car. a) Compare the magnitude of the force on the truck to the force on the car during the collision. Explain your reasoning. b) Compare the magnitude of the acceleration of the car to the truck during the collision. Explain your reasoning.

11. Two boxes sit on a table and are in contact with each other as shown. A force F is exerted as shown in the diagram. Draw a free body diagram for each of the boxes.

12. A 1200 kg car starts from rest and accelerates to a speed of 30 m/s in a time of 15 s. a) Sketch the situation. Indicate the net force on your diagram. b) Explain how you can find the net force acting on the car. c) Draw a free body diagram for the car. d) Find the magnitude of the net force acting on the car.

13. A car travels at a constant velocity of 30 m/s due west. a) What is the net force on the car? b) How do you know?

14. A 3 kg block slides down a rough plane inclined at an angle of 27°. a) Sketch the situation. b) Draw a free body diagram for the block. c) If the acceleration of the block is 2.5 m/s², find the coefficient of kinetic friction.

Problems from the text

Ch.3 #Multiple choice 1,2,4 Problems 7,25,31,43,55,71

Ch. 4 # Conceptual Questions1,8,13 Multiple Choice 1,14 Problems 14, 21,35,61,75,87,99,113 All problems must include sketch and FBD