ENERGY AND ITS CONSERVATION (K) KEY

Size: px

Start display at page:

Download "ENERGY AND ITS CONSERVATION (K) KEY"

Emory Stanley
7 years ago
Views:

1 ENERGY AND ITS CONSERVATION (K) Y. Natasha weghs 530 N. What s her knetc energy as she sws at a constant speed, coverng a dstance o 7 n.0 n? x v t 7 n.0 n 60 s. /s F g g F g g v Fv g g (530 N)(. /s) 9.8 N/kg 39 J. A 6.00-g block, ntally at rest, s pulled to the rght along a rctonless horzontal surace by a constant horzontal orce o.00 N or a dstance o 3.00 c. a. What s the work done by the orce? W Fx (.00 N)(3.000 ) J b. What s the change n the knetc energy o the block? W J c. What s the speed o the block ater the orce s reoved? v 0 v v ( J) kg /s 3. Zeke sldes down a snow hll on a rubber at. Zeke s ass s 76.0 kg and the ass o the at s.00 kg. Zeke starts ro rest at the crest o the hll. Frctonal orces ay be dsregarded. a. What s the change n the gravtatonal potental energy o Zeke and the at when they slde to.0 below the crest? Zeke at 78.0 kg PE PE PE gh gh gh (78.0 kg)(9.8 N/kg)(.0 ) 97 J b. What s the change n the knetc energy o Zeke and the at when they slde to.0 below the crest? PE PE PE PE (PE PE ) PE 97 J c. How ast are Zeke and the at ovng when they are.0 below the crest? v 0 v v (97 J) 78.0 kg 4.85 /s 4. As shown below, a 450-kg roller-coaster car starts ro rest at pont A at a heght o 47, rolls down the track, reachng pont B at a speed o 5 /s, and then rolls up a second hll where t reaches a heght o 3 beore cong to rest (at pont C). What are the gravtatonal potental energy and knetc energy o the car when t s at ponts A, B, and C?

5. An arrow wth a ass o 30 g s shot straght up nto the ar and reaches a heght o 50 beore stoppng and allng back to the ground. a. How uch work s done by gravty as the arrow reaches ts axu heght?

2 5. An arrow wth a ass o 30 g s shot straght up nto the ar and reaches a heght o 50 beore stoppng and allng back to the ground. a. How uch work s done by gravty as the arrow reaches ts axu heght? W g gh (0.3 kg)(9.8 N/kg)(50 ) 470 J b. I the arrow s knetc energy s zero at ts axu heght, calculate the ntal velocty o ths arrow as t s shot ro the ground. W g, and 0 J 6. Roht can consstently throw a 0.00-kg ball at a speed o.0 /s. On one such throw, Roht throws the ball straght upward and t passes the top o a lagpole when t s 6.00 above the ball s ntal poston. a. What s the ball s gravtatonal potental energy when t passes the top o the lagpole? (Assue the ball s ntal gravtatonal energy s 0 J.) PE gh lagpole (0.00 kg)(9.8 N/kg)(6.00 ).8 J b. What s the ball s knetc energy as t passes the top o the lagpole? PE PE PE 0 Pont A: PE A.0 5 J A 0 Pont B: PE B 0 B.40 5 J Pont C: PE C.00 5 J C 0 PE v (0.00 kg)(.0 /s).8 J.6 J PE c. What s the ball s velocty as t rst passes the top o the lagpole? v v (.6 J) 0.00 kg 5. /s, upward d. What s the axu heght to whch the ball wll rse? PE PE

3 PE 0; 0 snce v 0 at axu heght PE gh ax v v hax g (.0 /s) (9.8 N/kg) In a hardware store, pant cans, whch wegh 46.0 N each, are transported ro storage to the back o the pant departent by placng the on a rap that s nclned at an angle o 4.0 above the horzontal. The cans slde down the rap at a constant speed o 3.40 /s and then slde onto a table ade o the sae ateral as the rap. How ar does each can slde on the table s horzontal surace beore cong to rest? On the rap, usng a coordnate syste n whch the postve x-axs s orented down the rap: y-drecton: F net, y a y 0 F N F gy 0 F N F gy g cos F k F N k g cos x-drecton: F net, x a x 0 F gx g sn F gx F 0 g sn k g cos 0 sn k tan cos On the table: y-drecton: F N g F k F N k g W horzontal surace, whch exerts a constant rctonal orce on the toboggan. When the toboggan s released ro a heght o 5.0, t travels 6.0 along the horzontal surace beore cong to rest. Fro what heght should the toboggan be released so that t stops ater travelng 0.0 on the horzontal surace? W F x PE gh gh x F x s proportonal to h, so to ncrease x ro 6.00 to 0.0, h ust ncrease ro 5.0 to 0.0 (5.0 ) 6.00 h Meena releases her 0.5-kg toboggan ro rest on a hll. The toboggan gldes down the rctonless slope o the hll, and at the botto o the slope t oves along a rough

Homework: 49, 56, 67, 60, 64, 74 (p. 234-237)

Homework: 49, 56, 67, 60, 64, 74 (p. 234-237) Hoework: 49, 56, 67, 60, 64, 74 (p. 34-37) 49. bullet o ass 0g strkes a ballstc pendulu o ass kg. The center o ass o the pendulu rses a ertcal dstance o c. ssung that the bullet reans ebedded n the pendulu,