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# 有關普通物理學的問題...

4.During a panic stop，a car decelerates at 7.00 m/s2.（a）What is the angular acceleration of its 0.280 m radius tires，assuming they do not slip on the pavement？（b）How many revolutions do the tires make before coming to rest，given their initial angular velocity is 95.0 rad/s？（c）How long does it take？（d）What distance does the car travel in this time？（e）What was its initial velocity？（f）Do the values obtained seem reasonable，considering that this is a panic stop？

5.Olympic class ice skaters are able to spin at about 5 revolutions per second.（a）What is a 5.00 rev/s angular velocity in rad/s？（b）What is the centripetal acceleration of the skater’s nose if it is 0.120 m from the axis of rotation？（c）An exceptional skater named Dick Button was able to spin much faster in the 1950s than anyone since--- at about 9 revolutions per second！What was the centripetal acceleration of the tip of his nose, assuming it is at 0.120 m radius？（d）Comment on the magnitudes of the accelerations found. How many times the accelerations of his rose compare to gravity?. It is reputed that Button ruptured small blood vessels in his spins.

### 1 Answer

- Eric WangLv 71 decade agoFavorite Answer
4.

A) a= rα → 7=0.28*α → α= 25 rad/s²

B) ωt²=ω0²+2αθ→ 0=95²-2*25*θ→θ=180.5 rad=28.73 rev

C) ωt=ω0+αt → 0=95-25*t → t=3.8 sec

D) S = rθ=0.28*180.5= 50.54 m

E) V= rω=0.28*95=26.6 m/sec

F) 不合理,緊急煞車滑行了50多米,耗時近4秒.

5.

A) 5 rev/s=5*2π rad/s=31.4 rad/s

B) 向心加速度= rω²=0.12*31.4²=118.3 m/s²

C) 9 rev/s=9*2π=56.5 rad/s

向心加速度= rω²=0.12*56.5²=383.7 m/s²

D) 383.7/9.8= 39 → 地心引力的39倍