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HW 1_cont - Part C At what time(s do the two rockets have...

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Unformatted text preview: Part C At what time(s} do the two rockets have the same acceleration? Answer: At no time shown in the figure. Hint: It is because the rocket B is moving with constant velocity so it has acceleration zero but the rocket A is accelerating continuously. The motion of the rocket labeled A is an example of motion with uniform (i.e., constant} Answer: Non zero acceleration. Hint: The displacement of the rocket A is different at same interval of time so the displacement and velocity aren’t constant. But the displacement is changing with time so does velocity and hence it has non zero acceleration. The motion of the rocket labeled B is an example of motion with uniform (i.e., constant} Answer: Velocity Hint: The displacement of the rocket B is same at any equal interval of time. Since velocity' = distance travelled! time taken, velocity is same between at any equal interval of time. At what time{s) is recket A ahead cf recket B? Answer: Before t=l and after t=4 Hint: From the figure it is clear that rocket A is ahead cf rocket B at t=0 and F5. Cunverting Units: The Magic of 1 How many centimeters are there in a length seen inches? Express your answer in centimeters to three significant figures. Answer: 1331‘.) inches Hint: We knew 1 inch: 2.54 cm. That means 1'20 inches: 720 X 2.54cms=1828.8cms. There are 5 signifith figures in the answer. Se we round up to 3 significant figures and get the answer 183i] inches. Part B Suppose that a particuiar artillery piece has a range R = LUZSX l D yards. Find its range in miles. Use the facts that 1 mile =528i} fl and 3 fl = 1 yard. Express your answer in miles in three significant figures. Answer: 1.025X104 yards =5.82 miles l-iint: First we canvert yard inte feet: Lessxic“ yards =1.ezsx1e“ x s fl{Since 1 yard =3 a) =3esse a New we cenven feet inte miles: sesse a= setswsssc miles (Since 1 mile =szse a) =5.3233635.....mi1es There are many significant digits in abuse answer. 30 we rennd up in 3 significant figures and get the answer 5.82 miles. What is the speed of a car going v= 1 mph in SI units? Notice that you will need to change from miles to meters and from hours to seconds. You can do each conversion separately. Use the facts that 1 mile = 1639 m and 1 hour =3 fiflfls Express your answer in meters per second to three significant figures. Answer: v =0.447 mfs Hint: First we convert mile into m: 1 mile =1609 n1 Then we convert hour into sec: 1 hr=3 600 sec Thus 1 mile! hour= 1609 W360i} sec =U.4469444.....mfsec There are many significant digits in above answer. So we round up to 3 significant figures and get the answer 0. 44? mfsec. Significant Figures To seven significant figures, the mass of a proton is 1.672623 X 10‘ kg. Which of the following choices demonstrates correct rounding? Check all that apply. Answer: 1.67 2: “r1? kg Hint: The number 1.672 X 10%? is incorrect because when we round to four significant figures we get 1.63 x in”, not 1.6?2 x in”. Similarly, 1.6?263 X 111'“ is incorrect because when we round to six significant figures we get 1.5?262 x 10'”, not 1.6?263 3: 10'“. Part B To eight significant figures, Avogadro's constant is 6.9221367 X1 [J mol‘ . Which of the following choices demonstrates correct rounding? Check all that apply. Answer: 6.022 X ll] ‘3 met" an x in *3 mol'l 6.02214); to *3 mol'l Hint: All these options are correct; they represent different levels of precision, first with 4 significant figures, second with 1 significant figure and third with 6 significant figure rum... 5: Problem 1.45 l' iThe figure below is a motion diagram. Write a one or two sentence "story“ about Ia rent object that has this motion diagram. Your stories should talk about people i” objects by name and say what they are doing. A car starts coasting at an initial speed of 30mt'see up a 1D" incline. 230 m up the incline the road levels out to a flat road and the car 1 | l 1 Answer: l | continues at a reduced speed along the road. I _©__. Hint: The velocity of the car is not increasing at the flat road so the car isn‘t accelerating along the flat road so the second option is incorrect. The initial velocity of car is not is not zero so the third option is also incorrect. The first option mentioned above in answer is correct . Conce-tual I uestion 1.5 Does the object represented in the figure have a. positive or negative value of ac? Assume that v-axis ponits upward. Answer: Positive. Hint: The velocity is decreasing downward so the object is retarding and hence the acceleration is in opposite direction to that of velocity ie in upward direction along positive 3* axis. Thus acceleration is positive. Problem 1.12 Part A . . . t . . Figure shows two dots eta motion diagram and vector 13. Draw the vector '33 if the acceleration vector u at dot 3 points to the tight. Draw the vector with its tail at the dot 3. The orientation of your vector will be graded. The exact lengtlt ofvour vector 1will not be graded but the relative length of one to the other will be graded. Anwcr: Hint : The acceleration vector at point 3 is pointing toward right ie. along the direction opposite to the velocity,r .That means the body is retarding and hence its velocityF is decreasing. So the new velocit}r vector has smaller magnitude and hence shorter in length. Part E Figure shows two dots of a motion diagram and vector in. Draw the vector t":l’if the acceleration vector n at dot 3 points to the left. Draw the vector with its tail at the dot 3. The orientation of your vector will be graded. The exact length of your vector will not he graded but the relative length of one to the other will be graded. %-—-—-——-..(—__._. 5 a Hint: The acceleration vector at point 3 is pointing toward left is along the direction of velocity. That means the body is accelerating and hence its velocity.r is increasing. So the new velocity vector has greater magnitude and hence it is longer . Problem 1.13 The figure [Intro 1 figgfl} shows the motion diagram of a drag weer. The camera took one fi'ame ever).r 2 s. 2.“... .JIH'I- .f_-'u- :—:-'In'.'l- Make a position—versus—time graph for the drag racer. {a If film?) //’Q X . So -I- Mia-u- ———1— n. i: 1, In 11. "-1 Jr, Hint: Ema £5.) “a Here we plotted the graph according to following datas: Ffls,x=flm. t=25,x=2flm. 1:45., x=1flflm t=fis,x=2flflm t=Bs,x=4flIflm FIDax=52flm F125, x=fiflfls 1:143, x=T3flm Here fiom t=[l to t=3 the body is accelerathig so it is following almost parabolic path but from I=E to PM it is retarding. ...
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