10판/3. 벡터

3-42 할리데이 10판 솔루션 일반물리학

짱세디럭스 2019. 8. 12. 19:08

{d1=(4.0[m])i^+(5.0[m])j^d2=(3.0[m])i^+(4.0[m])j^\begin{cases} \vec d_1 = (4.0 \ut{m})\i + (5.0 \ut{m})\j\\ \vec d_2= (-3.0 \ut{m})\i + (4.0 \ut{m})\j\\ \end{cases}
(a) d1×d2=?\vec d_1 \times \vec d_2=? d1×d2=i^j^k^450340=5040i^+0403j^+4534k^=31k^ \begin{aligned} \vec d_1 \times \vec d_2=&\begin{vmatrix} \i & \j & \k\\ 4&5&0\\ -3&4&0\\ \end{vmatrix}\\ =&\begin{vmatrix} 5&0\\ 4&0\\ \end{vmatrix}\i+ \begin{vmatrix} 0&4\\ 0&-3\\ \end{vmatrix}\j+ \begin{vmatrix} 4&5\\ -3&4\\ \end{vmatrix}\k\\ =&31\k \end{aligned}
(b) d1d2=?\vec d_1 \cdot \vec d_2=? d1d2=4(3)+54=8.0 \vec d_1 \cdot \vec d_2=4\cdot(-3)+5\cdot4=8.0
(c) (d1+d2)d2=?(\vec d_1+\vec d_2)\cdot \vec d_2=? (d1+d2)d2={(43)i^+(5+4)j^}d2=1(3)+94=33 \begin{aligned} (\vec d_1+\vec d_2)\cdot \vec d_2=&\bra{(4-3)\i+(5+4)\j}\cdot\vec d_2\\ =&1\cdot(-3)+9\cdot4\\ =&33 \end{aligned}
(d) d1\vec d_1d2\vec d_2방향 성분 d1=42+52=41d_1=\sqrt{4^2+5^2}=\sqrt{41} d2=(3)2+42=5d_2=\sqrt{(-3)^2+4^2}=5 cosϕd1d2=d1d2d1d2=8541 \begin{aligned} \cos\phi_{d_1d_2}=&\frac{d_1\cdot d_2}{d_1d_2}\\ =&\frac{8}{5\sqrt{41}} \end{aligned} d1cosϕd1d2=418541=85=1.6 \begin{aligned} d_1\cos\phi_{d_1d_2}=&\sqrt{41}\cdot\frac{8}{5\sqrt{41}}\\ =&\frac{8}{5}\\=&1.6\\ \end{aligned}