7:51AM Sat Mar 9 Qe LX) S PV B 2ag HCHW Ch 2 (31).pdf Oy N 25.C. a. What is \"free fall motion\". Describe it in a short sentence. b. Suppose that the positive axis is upward and negative axis is downward. Seen is a snapshot of a rock executing free fall motion. What is sign of its velocity and acceleration? Is the rock slowing down or speeding up? Explain how you know. c. When the rock reaches its maximum height what is the value of its velocity at that moment? d. When it reaches maximum height, its acceleration is still =9.8 m/s?: yes, or no? e. True or False: to solve free fall motion problems, use the 4 kinematic equations for constant acceleration and simply replace a with g, that is to say a = 9.8 522 f. Look at the notes: we see that the letter "g" is the magnitude of the acceleration vector. As a magnitude which is correct: g =9.8 m/s? or g = 9.8 m/s? ? What is true about the sign of the magnitude of any vector? g. Using the standard direction of north/south axes where positive is up, when an object is in free fall is the vector componenta = g = 9.8 Sz ora=g = 9.8?2 ? 26.C. a). The \"magnitude\" of a vector is its size. Every magnitude is always positive: yes, or no? b). Given the coordinate system seen to the right, increasing numbers are upward and decreasing numbers are downward. Any vector with a negative value must point up or down? If a vector is a positive number, then which way does it point (north or south)? c). A student is doing a free fall problem on a baseball thrown vertically upward. He finds that at a particular instantthat x = 4+5m, v=+3m/s and a = 9.8m/s?. If you think of the origin as the earth's surface, then draw and lable the three vectors: position X , velocity , and acceleration d on the axis seen to the right. HELP: Recall that position vectors have their tail at the origin and tip at the object and velocity and acceleration are drawn on the object. 7:52AM Sat Mar 9 eoe Qe 2ag HCHW Ch 2 (31).pdf @] c). A student is doing a free fall problem on a baseball = thrown vertically upward. He finds that at a particular o instantthat x = +5m, v = +3m/s and a = 9.8m/s%. . @ e If you think of the origin as the earth's surface, then draw -' and lable the three vectors: position X , velocity , and acceleration @ on the axis seen to the right. " HELP: Recall that position vectors have their tail at the o origin and tip at the object and velocity and acceleration are drawn on the object. 2 d). For the numbers given in part (c), is the object slowing down or speeding up? Explain how you know with a short sentence. e). Astudent makes the statement \"if at an instant, the accleration and velocity of an object have opposite signs then the object is slowing down\". Is he correct? Yes, or no? f). A student makes the statement \"if at an instant, the accleration and velocity vectors point in the same direction, then the object is slowing down\". He is incorrect. Correct his statement. 27.21. Aballis thrown into the air with an initial speed vy =19 m/s from the height of a person's head, h = 1.6m. Choose the positive direction of the axis as upward like in the previous problem and the origin to be ground level. a. How high above the ground does the ball travel before turning around? : b. How long is the ball in the air? o . What is the acceleration and velocity at 1.6s? d. What is the acceleration and velocity at 2.3s? oo e. What is the ball's velocity and speed when it hits the 19m/s ground? I HELP: speed is a scalar and represents the magnitude of the velocity vector, so it is always positive. Speed can be found, 4 re like all magnitudes for one-dim vectors, by taking the absolute ik value of the vector. "b 28.22. a. Our class meets from 7pm to 10pm. What is the duration At (i.e., elapsed time) b. Suppose that someone in the class had a stopwatch and as soon as class started, he used the stopwatch to keep track of class time. What number does any stopwatch start at when you hit start? What number would the stopwatch read at the end of class? c. You can see that parts (a) and (b) give the same answer of 3 hours True or false: when using any physics equation that involves time, if the student always sets the initial time to 0, then At gives the same number as t. AT d. Inchapter 16 we will study the Heat Conduction Equation Ait =-A4 E . In this equation T is temperature and t is time. Given your answer to part (c), how might you rewrite this equation for the time part? 12 Q Notifications S PV B AN