HITT RF Remote Login Procedure:

Transcription

1 HITT RF Remote Login Procedure: The radio channel number for this room is 07 (zero, seven). It is STRONGLY recommended to login your remote for every class just to be sure it is on the correct radio channel and working before class. 1. PRESS AND HOLD THE DOWN ARROW KEY until the GREEN light on the remote turns RED. 2. PRESS THE 0 KEY and you will see the RED light flash GREEN. 3. PRESS THE 7 KEY and you will see the RED light flash GREEN. 4. PRESS AND RELEASE THE DOWN ARROW KEY again and you will see the red light search for the receiver, if it BLINKS GREEN MULTIPLE TIMES you are logged in.

2 Phy 2053 Announcements Exam 1 Feb 17 Wednesday, 8:20 10:10 pm Please get there at least 10 minutes early Covers Chapters 1-5 (includes Lecture on Feb 11 Th) Room assignments If your last name begins with A through O, you should go to Carleton 100 If your last name begins with P through Z, you should go to McCarty C 100 You will be allowed one handwritten formula sheet (both sides) Sample exam from last year posted on website. Previous exams & solutions available at Target copy.

3 Last name, then first name Test number

4 Scantron Test number

5 20 questions, multiple choice There is only one correct answer to the following question. (It is not a freebie.) In order to receive credit for this problem, you must correctly code ( bubble in") your UFID and your 5-digit test number (located at the top left and right hand corners of this test) onto your scan sheet and also select the correct response below. Please check now that you have correctly coded your exam number on the scan sheet. (1) I have correctly bubbled my UFID number and 5-digit test code. (2) I won't do this because I don't need really the credit. (3) I don't know what my UFID number is. (4) I can't read my test code. (5) I don't understand what is being asked. If your UFID and 5-digit test number is not entered correctly on your exam, you will not get credit for this question

6 Only the scantron will be graded. What you marked on the exam will NOT count. However, please circle your answer on the exam as well, in case the scantron is lost. (1) I have correctly bubbled my UFID number and 5-digit test code. (2) I won't do this because I don't need really the credit. (3) I don't know what my UFID number is. (4) I can't read my test code. (5) I don't understand what is being asked.

7 Exam 1 Phy 2053 Announcements Bring UFID or driver s license. Bring calculator, pencil and eraser. To make the exam fair to everybody, you must stop writing when the proctors announce that time is up. We will regard it as cheating if you continue to write. Stay in your seat until your exam is collected. If you finish early, raise your hands; proctors will come to collect it. If you want to avoid the long wait at the end, either (a) come early and sit at the front or (b) finish early

8 Phy 2053 Announcements Exam 1 In class review on Feb 16 Tuesday during lecture (Prof. Chan) We are trying to get a room for an optional review session (Prof. Acosta) for the evenings of Feb 15 Monday or Feb 16 Tuesday. How many of you will attend if we can find a room?

9 Spring Force Hooke s Law gives the force F = - k x F is the restoring force F is in the opposite direction of x k is spring constant k is larger for a stiffer spring x = 0 is the equilibrium position Slope = -k F x

10 Kinetic and Potential Energy Kinetic Energy: potential Energy: KE = 1 mv kx PE = mgh 2 g PEs = gravitational 2 spring Mechanical energy is conserved if there are no non-conservative forces (e.g. friction) ( KE + PE + = + + PE ) (KE PE PE ) g s i g s f

11 Example #5-39 The launching mechanism of a toy gun consists of a spring of unknown spring constant. If the spring is compressed by x = m and the gun fired vertically as shown, the gun can launch a 20.0 g projectile from rest to a maximum height of 20.0 m above the equilibrium position of the spring (x=0). (a) Find the spring constant, and (b) find the speed of the projectile as it moves through the equilibrium position of the spring.

12 Power The rate at which energy transfer takes place P Work F x = = = t t SI units are Watts: 1 W = 1 Fv J kg m = 1 3 s s 2 Motors (US): ft lb 1 hp = 550 = s 746 W KW-h is a unit of energy (check your electric bill!)

13 Example #5-53 The electric motor of a model train accelerates the train from rest to m/s in 21 ms. The total mass of the train is 875 g. Find the average power delivered to the train during the acceleration. (Assume the train is on a level track.)

14 Work done by a constant force W (Fcos θ) x Assume F is constant and parallel to x (cos θ= 1) F Work done by F = area under graph of F vs x x x

15 Work Done by Varying Forces The work done by a variable force acting on an object that undergoes a displacement is equal to the area under the graph of F x versus x

16 Work done pulling on a spring Spring is slowly stretched from 0 to xmax r F applied r = - F = kx s Area under the triangle = W = ½kx² Also equal to PE of spring

17 5-60 (modified) An object of mass 3 kg is subject to a force Fx that varies with position as shown in Figure. (a) Find the work done by the force on the object as it moves from x = 0 to x = 15 m. If the object has a speed of 0.5 m/s at x = 0. Find its speed at x = 15 m