Physics I (Navitas) EXAM #1 Fall 2015

Transcription

1 Physics I (Navitas) EXAM #1 Fall 2015 Name, Last Name First Name Student Identification Number: Write your name at the top of each page in the space provided. Answer all questions, beginning each new question in the space provided. Show all work. Show all formulas used for each problem prior to substitution of numbers. Label diagrams and include appropriate units for your answers. You may use an alphanumeric calculator (one which exhibits physical formulas) during the exam as long as you do not program any formulas into memory. By using an alphanumeric calculator you agree to allow us to check its memory during the exam. Simple scientific calculators are always OK! SCORE 1. (15) 2. (20) 3. (20) 4. (20) Total Score (out of 75 pts) Total Score (scaled up to 100 pts)

2 Problem 1: (15 points) - 3 pts each -- No partial credit on this problem only. Circle the letter corresponding to the most correct answer The figure shows the position of an object (moving along a straight line) as a function of time. Assume two significant figures in each number. Which of the following statements about this object is true over the interval shown? A) The object is accelerating to the left. B) The object is accelerating to the right. C) The acceleration of the object is in the same direction as its velocity. D) The average speed of the object is 1.0 m/s. 1-2 The graph shows the position versus time for an object during the time interval of t = 0.0 s to t = 9.0 s. (Assume that all numbers are accurate to two significant figures.) Which of the following results are correct according to the figure? A) average speed = 0.11 m/s; average velocity = 0.44 m/s B) average speed = 0.77 m/s; average velocity = 0.11 m/s C) average speed = 0.17 m/s; average velocity = 0.89 m/s D) average speed = 0.56 m/s; average velocity = 0.11 m/s E) average speed = 0.89 m/s; average velocity = 0.56 m/s

3 The displacement of a particle is given by: yt ( ) = 0.4t 7t + 4t 3 where y is in meters and t in seconds. Which of the following is correct? A) acceleration = 2.4t + 11 m/s 2 B) velocity = 2 1.2t + 14t 3 m/s C) acceleration = 14 m/s 2 D) acceleration = 2.4t 14 m/s 2 E) velocity = 2 t + 14t 3 m/s 1-4 An object moves at a constant acceleration a in a circular path of radius r. Which of the following is the object s linear velcity. A) a r B) a / r C) r / a D) sqrt (a / r) E) sqrt (a r) 1-5 Two children are riding on a merry-go-round. Child A is at a greater distance from the axis of rotation than child B. Which child has the larger angular speed? A) Child A B) Child B C) They have the same non-zero angular speed. D) They have the same zero angular speed. E) There is not enough information given to answer the question.

4 For problems 2, 3 and 4 NO credit will be given for just correct answer without appropriate formulae/logic. Circle your numerical answers. 4 Problem 2: (20 points) The total stopping distance (for maximum braking acceleration) of a car traveling at a speed of 30 m/s is 70 m which includes the distance traveled during the driver s reaction time of 0.55 s. A) Determine the distance the car travels during the driver s reaction time. B) Determine the maximum braking acceleration. C) Draw a motion diagram of the car s travel for parts (A) and (B) - indicating the velocity and acceleration vectors. D) Suppose that the same car was traveling at 40 m/s, determine the new total stopping distance under maximum braking acceleration. E) For the motion described in part D) determine the time elapsed while under braking acceleration.

5 Problem 3: (20 points) 5 Consider the following two vectors: A= 4iˆ 2ˆj B= 3iˆ+ 5ˆj R= A 4B A) Determine the magnitude and direction of the two vectors, A and B. B) Determine the components for the resultant vector R= A 4B. C) Determine the magnitude and direction of the vector R. D) Draw a coordinate system and draw all three vectors on it (start each vector at the origin).

6 Problem 4: (20 points) 6 A projectile is shot upward from a depth of 100 m (i.e. below the ground). A) Determine the maximum height of the projectile (above the ground) if the initial vertical component of its velocity is 80 m/s. B) Determine the initial angle that the projectile is shot at, if the initial speed is 90 m/s. C) Given that the projectile travels 620 m horizontally before it hits the ground. Determine the time the projectile is in the air. Hint: First find the initial horizontal component of the velocity. D) Determine the velocity vector of the projectile as it hits the ground. Express this in unit vector notation (i.e. in ı, ȷ form). Determine direction of the projectile as it hits the ground.