ashoksirphysics by ashok kumar

ashoksirphysics

KINEMATICS Airbag 3

20 v (m/s)

.01 .02 .03 .04 .05 t(s) Three different models of airbags were tested using identical crash test dummies. Sensors measured the velocity of the crash test dummy as a function of time, when the car crashed at 20 m/s into a brick wall. The shown velocity vs, time graphs resulted. Time t = 0 is the moment the car crashes. 6.

All three airbags are the same size and shape. Which one inflates most quickly? (A) Airbag 1 (B) Airbag 2 (C) Airbag 3 (D) We cannot determine the answer from the given information.

Let amax denote the largest instantaneous acceleration that the crash test dummy experiences during the crash. The best airbag is the one for which amax is as small as possible. Which airbag is best? (A) Airbag 1 (C) Airbag 3

For airbag 2, which of the following graphs best represents the position of the crash test dummy as a function of time? Let x = 0 m be the dummy’s position at time t = 0s.

.01 (A) A 9.

time(s)

.01

(B) B

Position

(B) Airbag 2 (D) We cannot determine the answer from the given information.

.01

time(s)

.01 time(s)

(D) D

For airbag 2, approximately how much distance does the dummy cover between the moment the car crashes and the moment the dummy first makes contact with the airbag? (A) 0.2 m (B) 0.4 m (C) 0.6 m (D) 1.0 m THE NEXT QUESTIONS REFER TO THE FOLLOWING PASSAGE Recently, college teams from all over the country sent tennis players to participate in a series of experiments conducted by the Physical Education Department of a major university. A variety of coaching methods was used to improve the players’ serves, described below. Experiment 1 Two groups of 50 tennis players worked on the speed of their basic serves for two weeks. one group consisted solely of right-handed players; the other consisted solely of left-handed players. Half of each group watched videos of a right-handed tennis coach. Each player was told to pattern his or her serve on that of the coach in the video. The players received no verbal or physical guidance. the average speed of each player’s serve was measured at the beginning and end of the two-week period, and changes were recorded in Table 1.

Table 1 Players' handedness Right Right Left Left

Coach's handedness Right Left Right Left

Average change in speed (mph) 5 2 -1 8

Experiment 2 For two weeks, a second group of 100 right-handed tennis players watched the same videos of the righthanded tennis coach. The coach also physically guided 50 of the those players through the motions of the serve. Again, no verbal instruction was given during the experiment. The average speed and accuracy of each player’s serves were recorded at the beginning and end of this two-week period. The results are recorded in Table - 2.