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Physics 7A Section 1 Fall Semester 2003 First Midterm Sept. 29, 2003 (6:107:40 pm)
Instructions
1. This is a closed hook exam. You are allowed to bring along on!  one 3’56” "cheat
sheet", pens, pails. scientiﬁc calculator, and blue books.
2. Read all questions carefully. Attempt the easiest ones ﬁrst.
3. Write your name, Discussion Section #1, GST name and SIDEI on the trip of'all
malet‘ials you intend to hand in and want to be graded,
4. While cleanliness and legibilily oryour hand—uniting will not get your extra credit,
they will help to make sure that your answers get the credit they deeerve In case you
make mistakes be sure to cross them out so they will not he mistaken as your answer. It helps to put _
I at box or Circle around your ﬁnal answers. 5. Partial credit You wiil get typically 90% of the total credit ifyou can either derive
your equations or show how the equation you wrote down from your cheat sheet can be
used to answer the question in terms of symbols you have deﬁned. When you Substitute
numbtars into these symbols to obtain a numerical answer, make sure that you specify
also the units. On the other hand, a pure numerical answer without caleutaiion to support
it will get no credit. You are provided with the following constants for your reference There. is no guarantee
that they will ail he required in solving, ﬂie problems.
Useful Constant: n=3.1415, greens W51; 1 mjle=].ol Km. 1 mph=0 44': mo; PaggZElfd ﬂuestion I (total: 20 Points] The advertisement for a sports car claims that the car can reach a speed of 60 miles per
hour (mph) from rest in 6 seconds. A sports utility vehicle (SUV) advertisement claims
that the car can reach a speed ot'oﬂ miles per hour [mph] in 13 seconds. (a) Assuming that both cars can achieve :r'usi‘anianetmsbJ their maximum acceleration,
What are the distances {expressed in miles) covered, respectively, by these two ears when
they reach 60 mph? (In) The masses of the sports car and SUV are [250 Kg and 2300 Kg. respectively. What
are the threes produced by the two car’s engine, assuming that there is not friction from
the road and no air resistance? (c) What will be the forces produced by the [we ear‘s engine to obtain the same
acceleration if there is friction and thal lite eoefl‘ieient of kinetic Friction between the rend
and the tires on both cars is 0.1? Air resistance is assumed to be negligible. Question 2 itnta]: 2t] Poinlsl An artillery wantto hit a target located at a distance of 1.8 Km away. (:1) Suppose the artillery can ﬁre shells with a maximum speed ot‘U.2 Kim’s what should
he the angle of“ tilt (G) of the canon to the ground in order that the shell will hit the target?
(b) What should he tilt of the canon in case the target is located on a slope inclined at 25"
to the horimnlal as shown in the figure? The distance between [he artillery and the
bottom ofthe slope is O. 5 Km while the target is at a distance of I. 3 Km from the bottom
of the slope. ll'you ﬁnd two amptnble tilt angles which one will you ehose assume lhai.
you have to ﬁre the canon? In this qu estion mgfect the height Ofelia tame: and moon and
also the air rea'istwtce. Target Artillery h——'1
0.5 Km Question 3 (total: 20 Point!!! A small block of mass 20 Kg is resting on a larger block of mass 30 Kg. The two blocks are testing on a table A force 'F is applied to the large block as shown in the figure on
next page. Pngg J of 4
(a) The TWO blocks famain Stationary with respect to the table until F=4O N when the lwo
blocks start to move together. What is [he caeﬁicient of static friction between the large
block and the table?
fh] Once the two blocks stm moving the cueﬂ'iuiem offriciion betwemi the large block
and the table quickly drops to the value 60.05 for kinetic friction, what is the
acceleratinn oft he two blocks?
(c) Suppose the coefﬁcient of static friction between the small block and the large block
is 0. ]. What will he the force when the small block starts to fly nfl'the large block? 20 Kg
30 Kg ﬂuﬁun 411mm: 20 Points} A windnw cleaner and his platform has a tnlal mass of I'm Kg. The plail‘orm is
suspended from a I'ricﬁuulcss and massless pulley,r by a. counter weight 0" 100 Kg. as
show in ﬁgure: Pulley
Gaunter
‘Window Weight
Cleaner
3: Platfoml Assume [hail the rope has no mass also. (3} HOW muCh force Shnuld the winduw ulmner apply to the rope in nrder that he can
raise himself slowly at n mnslanl speed? Gil? y'cmr answer 10 J .tfé‘miﬁcrzmﬁsmres, Page ~$ of 4 (b) Suppose the window cleaner is ascemﬂng with a constant speed 01113 "Us towards a
window at a distance of 5 m above him. What Force sh0uid he appiy new in order that
he will stopjust in Front. ofthe window? Give your answer m ]l .s'rgurﬁmnrﬁgurex. Question 51mm: 20 Points] Tn a Circus :1 dare—devil performer can go around a steel Spherical Gage (olfadius 3"— 10
meters) on a motor—cycle so fast that his molot—eycle becomes lloriwulal as shown in the
ﬁgure! The coeﬁ'leiems of static and kinetic friction between the motor—cycle and the
steel cage are (18 and [)5 respectively. (a) What is the speed of the motor—cyclist in order to ride around the cage in this
horizontal position“? {b} AS the motorcycle slows down the angle El} between the motorcyclist and the vertica]
deereaeee: From 90°. What should be the speed of The motorcyclist when t1) equals to 45". ———EN'D or QUESTIONS —————————— .......
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 Spring '08
 Lanzara
 Physics

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