a) No books or notes are permitted. b) You may use a calculator.

Transcription

1 PHYS 050 Sprng 06 Name: Test 3 Aprl 7, 06 INSTRUCTIONS: a) No books or notes are permtted. b) You may use a calculator. c) You must solve all problems begnnng wth the equatons on the Inormaton Sheet provded wth ths test. Please wrte down the equaton you are usng, or the prncple you are applyng to a gven stuaton. d) You must show your work to receve credt!!!! I a problem requres only a smple answer, you must explan your answer. Please show all o your work on the sheets provded (use the back necessary). d) Please draw a box or a crcle around each o your answers.

2 . A 50-kg grl rdes on a gant Ferrs wheel o radus 4 m whch makes revoluton every 75 seconds. (a) (5 ponts) What s the grl s speed n m/s? (b) (5 ponts) What s the angular momentum o the grl as she rdes? (c) (0 ponts) What s the apparent weght o the grl at the lowest pont n the rde? (Hnt: Her apparent weght s equal to the orce o the seat actng on her). (d) (0 ponts) I she elt weghtless at the top o the rde, how ast would she be movng? Note: Use your own experences to check your answers are reasonable.

3 . An 8-g bullet travelng at 50 m/s penetrates a 4.0-kg block o wood and emerges at 50 m/s. (a) (0 ponts) I the block was statonary when t was ht, how ast does t move mmedately ater the bullet emerges? (b) (0 ponts) Determne explctly whether ths s an elastc or an nelastc collson. (You must show your work!) 3

4 3. A potter works wth a unorm sold grndstone wheel that has a mass o 8 kg and a radus o 5 cm. The grndstone ntally rotates at 00 rev/mn. The grndstone s motor s turned o and the potter presses an nstrument perpendcular aganst the grndstone wth a orce o 40 N to brng t to a stop. The coecent o rcton wth the grndstone s 0.7. The grndstone can be consdered a unorm sold cylnder or whch I = ½ mr. (a) (0 ponts) What s the torque on the grndstone n stoppng t? (b) (0 ponts) Fnd the angular deceleraton o the grndstone. (c) (0 ponts) How long does t take the grndstone to stop? 4

5 4. A 30-kg chld runs around the edge o a playground merry-go-round. The merry-go-round has a mass o 00 kg and a radus o.0 m. Consder t to be a unorm sold dsk or whch I = ½ mr. The chld s observed to be runnng, relatve to the Earth, at a speed o 3.0 m/s whle the merry-go-round rotates n the opposte drecton makng one revoluton every sec. (a) (0 ponts) I the chld stops runnng, what s the angular speed o the chld plus merrygo-round combnaton? (b) (0 ponts) How much work s done as the chld stops runnng? 5

6 sn = opp/hyp cos = adj/hyp tan = opp/adj INFORMATION SHEET v v 0 at r r r s s N x x0 (v v0) t c = a + b x x0 v0t at r v k = k N r v lm 0 W = (F-comp.) x (d) = Fd x = x - x v v 0 ax a W net = KE = ½mv - ½mv 0 KE = ½ mv x x x v A cos t a lm x 0 U gravty = PE gravty = mgy F sprng = -kx x v lm A y Asn vac vab v bc 0 U sprng = PE sprng = ½kx v a t a lm 0 v A F net F ma tan A x A y A A y x W dw P F v dt v a c r E = E p = mv = s/r F c = ma c = mv t /r 0 p dp F ( ) t dt 0 0 = rfsn = rfsn = I; I = m r Impulse F 0 0 t KE = ½ I Impulse = p = mv - mv l rxp ; l rmv v t = r 0 F net = 0 P ntal = P L I nal a t = r a c = v t /r = r v v = -(v v ) g = 9.8 m/s = 3 t/s 6