10판/2. 직선운동

2-22 할리데이 10판 솔루션 일반물리학

짱세디럭스 2019. 7. 24. 20:02
x=ct2bt3x= ct^2 - bt^3 (a) Ans=c=? \Ans = c =? put kn=AnyNumber \put k_n = \text{AnyNumber} x=ct2bt3=k1[m]c(t[s])2b(t[s])3=k1[m](2221)c(t[s])2=k2[m]c(t2[s2])=k2[m]c=k2[m]t2[s2]c=k2t2[m/s2]\begin{aligned} x &= ct^2 - bt^3=k_1\ut{m} \\ &\Rightarrow c(t\ut{s})^2 - b(t\ut{s})^3 = k_1\ut{m} \cdots(2-22-1) \\ &\Rightarrow c(t\ut{s})^2 = k_2\ut{m} \\ &\Rightarrow c(t^2\ut{s^2}) = k_2\ut{m} \\ &\Rightarrow c = \frac{k_2\ut{m}}{t^2\ut{s^2}} \\ &\Rightarrow c = \frac{k_2}{t^2}\ut{m/s^2} \end{aligned} (b) Ans=b=? \Ans = b =? (2221),(2-22-1), c(t[s])2b(t[s])3=k1[m]b(t[s])3=k3[m]b(t3[s3])=k3[m]b=k3[m]t3[s3]b=k3t3[m/s3]\begin{aligned} \\ &c(t\ut{s})^2 - b(t\ut{s})^3 = k_1\ut{m} \\ &\Rightarrow b(t\ut{s})^3 = k_3\ut{m} \\ &\Rightarrow b(t^3\ut{s^3}) = k_3\ut{m} \\ &\Rightarrow b = \frac{k_3\ut{m}}{t^3\ut{s^3}} \\ &\Rightarrow b = \frac{k_3}{t^3}\ut{m/s^3} \end{aligned} (c)~(m) {c=3.0b=2.0 \begin{cases} c &= 3.0 \\ b &= 2.0 \end{cases} x=3.0t22.0t3x = 3.0t^2 - 2.0t^3 v=x˙= ⁣dx ⁣dt= ⁣d ⁣dt(3.0t22.0t3)=6t6t2\begin{aligned} v &= \dot x = \dxt{x} \\ &=\dt(3.0t^2 - 2.0t^3) \\ &= 6 t-6 t^2 \end{aligned} a=v˙= ⁣dv ⁣dt= ⁣d ⁣dt(6t6t2)=612t \begin{aligned} a &= \dot v = \dxt{v} \\ &=\dt(6 t-6 t^2) \\ &=6 - 12 t \end{aligned} {x=3.0t22.0t3v=6t6t2a=612t(2222)\therefore \begin{cases} x &= 3.0t^2 - 2.0t^3 \\ v &= 6 t-6 t^2 \\ a &=6 - 12 t \end{cases} \cdots(2-22-2) (c) tmaxx=?t_{\max x} = ? v=6tc6tc2=0 v = 6 t_c-6 t_c^2 = 0 tc=0,1(2223) t_c = 0, 1\cdots(2-22-3) a(tc)=(0,6),(1,6) a(t_c) = (0,6),(1,-6) {xLocalMin=x(0)xLocalMax=x(1) \therefore \begin{cases} x_{LocalMin} &= x(0) \\ x_{LocalMax} &= x(1) \end{cases} tmaxx=1[s] (t>0) \therefore t_{\max x} = 1\ut{s} \ (\because t>0) (d) Ans=04v ⁣dt=? \Ans = \int_0^4 \abs{v}\,\dd t =? (2223), (2-22-3), v={v,(0t1)v(1t) \abs{v} = \begin{cases} v, &(0 \le t \le1) \\ -v &(1 \le t) \end{cases} Ans=04v(t) ⁣dt=01v ⁣dt+14v ⁣dt=01v ⁣dt14v ⁣dt=[V]01[V]14=[x]01[x]14=[x(1)x(0)][x(4)x(1)]=2x(1)x(0)x(4)=82[m]\begin{aligned} \\ \therefore \Ans &= \int_0^4 \abs{v(t)}\,\dd t \\ &= \int_0^1 v\,\dd t+\int_1^4 -v\,\dd t \\ &= \int_0^1 v\,\dd t-\int_1^4 v\,\dd t \\ &= \[V\]_0^1-\[V\]_1^4 \\ &= \[x\]_0^1-\[x\]_1^4 \\ &= \[x(1)-x(0)\]-\[x(4)-x(1)\] \\ &= 2x(1)-x(0)-x(4) \\&=82\ut{m} \end{aligned} (e) Ans=x(4)x(0)={3.0(4)22.0(4)3}{3.0(0)22.0(0)3}=8.0×10[m]\begin{aligned} \Ans &= x(4)-x(0) \\ &=\{3.0(4)^2 - 2.0(4)^3\}-\{3.0(0)^2 - 2.0(0)^3\} \\ &= -8.0\times 10\ut{m} \end{aligned} (f)~(i) (2222), (2-22-2), v=6t6t2v = 6 t-6 t^2 (f)v(1.0)=6(1.0)6(1.0)2=0.0[m/s](g)v(2.0)=6(2.0)6(2.0)2=12[m/s](h)v(3.0)=6(3.0)6(3.0)2=36[m/s](i)v(4.0)=6(4.0)6(4.0)2=72[m/s]\begin{aligned} \, (f) \, v(1.0) &= 6(1.0)-6(1.0)^2 = 0.0\ut{m/s} \\ \, (g)\, v(2.0) &= 6(2.0)-6(2.0)^2 = -12\ut{m/s} \\ \, (h)\, v(3.0) &= 6(3.0)-6(3.0)^2 = -36\ut{m/s} \\ \, (i)\, v(4.0) &= 6(4.0)-6(4.0)^2 = -72\ut{m/s} \end{aligned} (j)~(l) (2222),(2-22-2), a=612t a =6 - 12 t (j)a(1.0)=612(1.0)=6.0[m/s2](k)a(2.0)=612(2.0)=18[m/s2](l)a(3.0)=612(3.0)=30[m/s2](m)a(4.0)=612(4.0)=42[m/s2]\begin{aligned} \, (j) \, a(1.0) &= 6 - 12(1.0) = -6.0\ut{m/s^2} \\ \, (k)\, a(2.0) &=6 - 12(2.0) = -18\ut{m/s^2} \\ \, (l)\, a(3.0) &= 6 - 12(3.0)= -30\ut{m/s^2} \\ \, (m)\, a(4.0) &=6 - 12(4.0)= -42\ut{m/s^2} \end{aligned}