b) (5) What is the magnitude of the force on the 6.0-kg block due to the contact with the 12.0-kg block?

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1 Geneal Physics I Exam 2 - Chs. 4,5,6 - Foces, Cicula Motion, Enegy Oct. 13, 2010 Name Rec. Inst. Rec. Time Fo full cedit, make you wok clea to the gade. Show fomulas used, essential steps, and esults with coect units and significant figues. Patial cedit is available if you wok is clea. Points shown in paenthesis. Fo TF and MC, choose the best answe. 1. (6) The diagam shows the foces acting on a ca acceleating to the ight. The pavement is level. F oad is the fiction foce of the oad on the ties, and F ai is the ai esistance. Select the coect elationship between the foce magnitudes. a) a. F oad > F ai b. F oad = F ai c. F oad < F ai b) a. F N > mg b. F N = mg c. F N < mg 2. (6) A ca is moving at constant speed up a θ = 30 incline; the foces ae shown on the diagam. Choose the coect elationships between the foce magnitudes. a) a. F oad = F ai b. F oad = F ai mg sin θ c. F oad = F ai + mg sin θ b) a. F N = mg b. F N = mg cos θ c. F N = mg sin θ 3. (16) A constant foce F 1 = 72.0 N is applied to a 6.00-kg block, which contacts a 12.0-kg block. They acceleate togethe on a hoizontal fictionless suface. a) (6) How lage is thei common acceleation? b) (5) What is the magnitude of the foce on the 6.0-kg block due to the contact with the 12.0-kg block? c) (5) What is the magnitude of the net foce on the 6.0-kg block? 4. (2) T F If the acceleation of a mass is zeo, then thee ae no foces acting on it. 5. (2) T F The foce fom the dive tain tuning the wheels is what acceleates a ca. 6. (2) T F A static fiction foce on a mass always pevents the mass fom moving. 7. (2) T F Eath s gavitational foce on you is geate than you gavitational foce on the Eath. 8. (2) T F Sliding on a fictionless incline, a box acceleates moe going downhill athe than uphill. 9. (2) T F On an incline with fiction, a sliding box acceleates moe going downhill athe than uphill. 10. (2) T F Fo contact between two given mateials, static fiction is stonge than kinetic fiction. 1

2 11. (10) A 2.2-kg fish is being pulled out of the wate, in such a way that the tension in the fishing line is 3.0 times its weight. Daw the foces acting on the fish (fee body diagam) and find the acceleation of the fish (magnitude and diection). 12. (14) A space station is a hollow cylinde of adius 440 m, that otates to simulate gavity by its centipetal acceleation. The astonauts live at the adius 440 m fom the cente, with thei heads pointing inwad and thei feet outwad! a) (6) What speed v should the otation give the astonauts so they feel like they ae in atificial gavity of stength 2.50 g (2.5 gavity on Eath)? b) (4) Find the peiod of the otation in seconds. c) (4) Find the otation speed in evolutions pe minute. 13. (2) The flying pig, suspended fom a cable (demo in lectue), moves at constant speed in a hoizontal cicle. The net foce on him must point a) along the cable. b) hoizontally, towads the cente of the cicle. c) vetically, due to his weight. d) none of these, because the net foce is zeo. 2

3 Name Rec. Inst. Rec. Time 14. (10) A physics student takes a 5.0-kg pail of wate connected on a ope, and swings it in a vetical cicle of adius 90.0 cm at a constant speed of 7.0 m/s. a) (5) When the pail passes its highest point, what ae the magnitude and diection of its acceleation? b) (5) When the pail passes its highest point, what is the tension in the ope? 15. (10) The acceleation due to gavity at the suface of a planet of mass M, adius R, is given by the expession, g = GM/R 2. On Eath, this value is g = 9.80 m/s 2. a) (4) If Eath s diamete wee half what it is, while keeping the same mass, what would g be in m/s 2? b) (6) Suppose a planet is discoveed that has a mass 12 times that of Eath, and a adius 2.0 times that of Eath. What is the value of g in m/s 2 on this planet? 16. (6) A 145-kg football playe applies a foce of 520 N hoizontally on the opposing 125-kg quateback, while pushing him backwads 3.3 m at constant speed befoe being tackled. How much wok did the tackle do while pushing? 3

4 17. (2) T F Fiction foces always do negative wok. 18. (2) T F A ca can acceleate faste if the fiction between the oad and its ties is smalle. 19. (2) T F The gavitational foce does positive wok on a ising object. 20. (2) T F Potential enegy stoed in spings is always negative. 21. (2) T F When ascending a flight of stais, you gavitational potential enegy deceases. 22. (2) A foce F acting though a displacement d does negative wok when a. F is paallel to d. b. F is pependicula to d. c. F is anti-paallel to d. 23. (18) A 2200-kg ca is initially coasting at a speed of 24 m/s when it comes to a θ = 12.0 incline. It coasts without fiction o ai esistance, up the incline. a) (6) How lage is the initial kinetic enegy of the ca, in kj? b) (6) Afte it tavels 75.0 m along the incline, how lage is the gavitational potential enegy of the ca, in kj? Take the zeo of PE to be at the bottom of the incline. c) (6) How fast is the ca coasting now afte it went 75.0 m along the incline? 24. (8) A 62-kg athlete uns up a flight of stais at constant speed, gaining an elevation of 50.0 m in 40.0 s. What was the aveage mechanical powe output of he body, in watts? Scoe = /132. 4

5 Pefixes a=10 18, f=10 15, p=10 12, n=10 9, µ = 10 6, m=10 3, c=10 2, k=10 3, M=10 6, G=10 9, T=10 12, P=10 15 Physical Constants g = 9.80 m/s 2 (gavitational acceleation) M E = kg (mass of Eath) m e = kg (electon mass) c = m/s (speed of light) G = N m 2 /kg 2 (Gavitational constant) R E = 6380 km (mean adius of Eath) m p = kg (poton mass) Units and Convesions 1 inch = 1 in = 2.54 cm (exactly) 1 foot = 1 ft = 12 in = cm (exactly) 1 mile = 5280 ft 1 mile = m = km 1 m/s = 3.6 km/hou 1 ft/s = mile/hou 1 ace = ft 2 = (1 mile) 2 /640 1 hectae = 10 4 m 2 Tig summay sin θ = (opp) (hyp), (adj) cos θ = (hyp), (opp) tan θ = (adj), (opp)2 + (adj) 2 = (hyp) 2. sin θ = sin(180 θ), cos θ = cos( θ), tan θ = tan(180 + θ), sin 2 θ + cos 2 θ = 1. Chapte 1 Equations Pecent eo: If a measuement = value ± eo, the pecent eo = eo value 100 %. Chapte 2 Equations Motion: v = x t, x = x x 0, slope of x(t) cuve = v(t). ā = v t, v = v v 0, slope of v(t) cuve = a(t). Fo constant acceleation in one-dimension: v = 1 2 (v 0 + v), v = v 0 + at, x = x 0 + v 0 t at2, v 2 = v a(x x 0 ). Fo fee fall on Eath, using an upwad y-axis, with g = 9.80 m/s 2 downwad: v y = 1 2 (v y0 + v y ), v y = v y0 gt, y = y 0 + v y0 t 1 2 gt2, v 2 y = v 2 y0 2g y. Chapte 3 Equations Vectos Witten V o V, descibed by magnitude=v, diection=θ o by components (V x, V y ). V x = V cos θ, V y = V sin θ, V = Vx 2 + V 2 tan θ = Vy θ is the angle fom V to x-axis. y, V x. Addition: A + B, head to tail. Subtaction: A B is A + ( B), B is B evesed. Pojectiles a x = 0, v x = v x0, x = x 0 + v x0 t. Fo a hoizontal x-axis. a y = g, v y = v y0 gt, y = y 0 + v y0 t 1 2 gt2. Fo an upwad y-axis. R = v2 0 g sin 2θ 0, Relative Motion V BS = V BW + V WS, (Fo level gound only.) B=Boat, S=Shoe, W=Wate. BS means boat elative to shoe, etc. Must be applied as a vecto equation! 5

6 Chapte 4 Equations Newton s Second Law: F net = m a, means ΣF x = ma x and ΣF y = ma y. Fnet = Fi, sum ove all foces on a mass. Fiction (magnitude): f s µ s N o F f µ s F N (static fiction). f k = µ k N o F f = µ k F N. (kinetic o sliding fiction) Gavitational foce nea Eath: F G = mg, downwad. Chapte 5 Equations Centipetal Acceleation: a R = v2, towads the cente of the cicle. Cicula motion: speed v = 2π T = 2πf, fequency f = 1 T, whee T is the peiod of one evolution. Gavitation: F = G m1m2 ; 2 g = GM, 2 whee G = Nm 2 /kg 2 ; Obits: v 2 = g = GM 2 ; v = Chapte 6 Equations GM. centipetal acceleation = fee fall acceleation. Wok & Kinetic & Potential Enegies: W = F d cos θ, KE = 1 2 mv2, PE gavity = mgy, PE sping = 1 2 kx2. θ = angle btwn F and d. Consevation o Tansfomation of Enegy: Wok-KE theoem: KE = W net = wok of all foces. Powe: P ave = W t, o use P ave = enegy time. Geneal enegy-consevation law: KE + PE = W NC = wok of non-consevative foces. 6

c) (6) Assuming the tires do not skid, what coefficient of static friction between tires and pavement is needed?

c) (6) Assuming the tires do not skid, what coefficient of static friction between tires and pavement is needed? Geneal Physics I Exam 2 - Chs. 4,5,6 - Foces, Cicula Motion, Enegy Oct. 10, 2012 Name Rec. Inst. Rec. Time Fo full cedit, make you wok clea to the gade. Show fomulas used, essential steps, and esults with