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# 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?

Update:

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• 1 decade ago

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