麵包
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麵包 asked in 科學其他:科學 · 1 decade ago

急!徵物理高手解題(20點)

1.An automobile travels on a straight road for 40km at30km/h. It then continues in the same direction for another 40km at 60km/h. (a)What is the average velocity of the car during this 80km trip? (b)What is the averge speed? (c)Graph x versus t and indicate how the average velocity is found on the graph?

2. The position of a particle moving along the x axis is given in centimeters by x =9.75+1.50t(三次方), where t is in seconds. Calculate (a)the average velocity during the time interval t = 2.00 s to t = 3.00s (b) the instantaneous velocity at t = 2.00s (c)the instantaneous velocity at t = 3.00s (d)the instantaneous velocity at t = 2.50s (e)the instantaneous velocity when the particle is midway between its positions at t =2.00s and t = 3.00s (f)Graph x versus t and indicate your answers graphically.

3. At a certain time a particle had a speed of 18m/s in the positive x direction, and 2.4s later its speed was 30m/s in the oppsite direction. What is the average acceleration of the particle during this 2.4s interval?

4. When startled, an armadillo will leap upward. Suppose it rises 0.544 m in the first 0.200s (a)What is its initial speed as it leaves the ground? (b)What is its speed at the height of 0.544m? (c) How much higher does it go?

能附上中文翻譯與各題詳解最佳!

拜託各位高手了~~

Update:

都沒人能幫忙嗎@@

1 Answer

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  • 1 decade ago
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    1. (a)平均速度=總位移/總時間=80/(40/30+40/60)= 40 km /hr

    (b)平均速率= 40 km /hr

    (c)我無法貼圖!請自己畫。

    2. x=9.75+1.5t3→ v=dx/dt=4.5t2

    (a) v2~3=[x(3)-x(2)]/(3-2)= 28.5 cm /s

    (b) v(2)=4.5*22= 18 cm/s

    (c) v(3)=4.5*32= 40.5 cm/s

    (d) v(2.5)=4.5*2.52= 28.125 cm/s

    (e) [x(3)+x(2)]/2=(9.75+1.5*23+9.75+1.5*33)/2=36→ x=9.75+1.5t3=36→ t=2.60 s→v(2.6)=4.5*2.62= 30.4 cm/s

    (f) 我無法貼圖!請自己畫。

    3. 平均加速度=速度差/時間=(-30-18)/2.4= -20 m /s2

    4. (a) h=v0t-(1/2)gt2→ 0.544=v0*0.2-(1/2)*9.8*0.22→ v0= 3.7 m /s

    (b) v=v0-gt=3.7-9.8*0.2= 1.74 m /s

    (c) v2=v02-2gH→ 0=3.72-2*9.8*H→ H=0.7 m

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