Multiple choice questions [70 points]

Transcription

1 Multiple choice questions [70 points] Answe all of the following questions. Read each question caefull. Fill the coect bubble on ou scanton sheet. Each question has exactl one coect answe. All questions ae woth the same amount of points. 1.. A ca stats fom point A, goes 50 km in a staight line to point B, immediatel tuns aound, and etuns to A. The time fo this ound tip is hous. The magnitude of the aveage velocit of the ca fo this ound tip is: A. 0 km/h v avg and 0 B. 50 km/h C. 100 km/h D. 00 km/h E. Cannot be calculated without knowing the acceleation Still efeing to the situation descibed in the pevious question, what is the aveage speed of the ca? A. 0 km/h B. d 50 km/h speed with d100 km and t hs C. 100 km/h D. 00 km/h E. Cannot be calculated without knowing the acceleation 3. A ball olls up a slope. At the end of 3 seconds its velocit is 0 cm/s; at the end of 8 seconds its velocit is 0 cm/s. What is the magnitude of the aveage acceleation (in cm/s ) fom the instant 3s to the instant 8s? A..5 B. 4.0 a avg C. 5.0 D. 6.0 E v 0 0, thus a avg 4 cm / s 8 3

2 4. As a ocket is acceleating veticall upwad at 9.8 m/s nea Eath's suface, it eleases a pojectile. Immediatel afte elease the acceleation (in m/s ) of the pojectile is: A. 9.8 down since the pojectile is fee falling (it is no longe subjected to an foce b the ocket). B. 0 C. 9.8 up D up E. None of the above 5. An object moves along the hoizontal axis as shown on the diagam. At which point o points is its acceleation zeo? A. C onl B. E onl C. B and D D. A and E The acceleation is 0 when the position vaies lineal with time (xvt+x 0 ). On the gaph, the acceleation is 0 wheeve x(t) is a staight line. E. B, D and E

3 6. A paticle initiall moving at 4.0 m/s along the x axis is unifoml acceleated at 3.0 m/s along the axis fo.0 s. The final speed of the paticle is A. 4.0 m/s B. 6.3 m/s vx 4.0 m / s C. 7. m/s v( t s) v x + v 4 + (3 ) v 3t D. 8.4 m/s E. None of these is coect. 7. -v 1 v The instantaneous velocit of a paticle at t1 is epesented b v1, and at t b v. Each heav gaph division is 10 m/s on each side. Let t1 1 s and t 7 s. Then the aveage acceleation of the paticle between time t1 and t is A. 18. m/s at 0º B m/s at 180º C m/s at 98º 5.00 m/s at 180º v v v1 D. a avg Constuct v as indicated above E m/s at 98º

4 8. The angle between vectos A and B is 30º, and thei sum is C. Which vecto diagam coectl descibes the vectos A, B, and C? A. 1 B. C. 3 D. 4 E In the diagam, A has magnitude 1 m and B has magnitude 8 m. The x component of A B is about A B x A m B. 4.0 m C. 4.5 m 1cos(45)-8cos(60) D m E. 0 m

5 10. Two objects, A and B, move with constant speed elative to a staight line. The stobe diagam shows the positions of the objects at instant 1-3, sepaated b one-second time intevals. (Note that each tick mak on the diagam epesents 5 metes.) 1 A A 3 A 5 metes B 3 B B 1 At instant what is the diection of the instantaneous velocit of object A in the fame of efeence of object B? A. to the left B. to the ight (see next question) C. Undefined: the velocit is zeo 11. Still efeing to the poblem of the pevious question, at instant, what is the magnitude of the instantaneous velocit of object A in the fame of efeence of object B? A. 0 m/s B. 10 m/s C. 0 m/s D. 30 m/s E. 50 m/s Since the velocities ae constant, instantaneous and aveage velocities ae equal. Compute the aveage velocit between fo instance instant t 1 and instant t A / B ( t ) A / B ( t1) ( 5) xˆ ( 1 5) xˆ v A B 50m / s xˆ / t t1 1 whee xˆ is a unit vecto diected to the ight.

6 1. A gil on a me-go-ound moves hoizontall in a cicle at constant speed. She tavels one fouth of a evolution, a distance of 5m along the cicumfeence of the cicle, in 5.0s. The magnitude of he acceleation is A m/s B. 1.3 m/s C. 1.6 m/s v (5/ 5) a π / R 5 π / D. 3.9 m/s E. 6.3 m/s

7 PROBLEM [40 points] A bo huls a stone with a sling shot at a fling line of Canada geese. The stone is thown at 30m/s veticall upwad exactl when the fist of the line of geese is ovehead (t0). The geese fl 4m/s, 10 m apat at an altitude of 5m (counted fom the position of the stone at t0). Take g10 m/s 5 m 1). [10 pts] If the bo misses the geese, when does the stone each its maximum height? 4 m/s 10 m 30 m/s x The velocit is 0 at t such that v 10 t + 30 t 3s ). [15 pts] When does the stone coss the path of the geese (make sue that ou count all possible cossings)? Solve 5m fo t 1 10t + 30t 5 t 1s and t 5s 3). [15 pts] Does the stone hit a goose; if so which one (fist goose is #1)? The position of goose n is given b x n 4t 10( n 1) To be hit the goose cosses the path of the stone (x n 0) at t1s o at t5s 14 at t1s, x n 0 n, no goose is hit since n must be an intege at t5s, x n 0 n 3, goose 3 is hit. 10