91影视

In the same manner that torque is the rotational equivalent of force, angular momentum is the rotational equivalent of linear momentum. In vector notation, angular momentum is given by

$\stackrel{鈫�}{L}=\stackrel{鈫�}{r}脳\stackrel{鈫�}{p}$

Here $\stackrel{鈫�}{r}$ is the position vector of the particle and$\stackrel{鈫�}{p}$ is the momentum vector of the given particle.

The travelling particle's direction is depicted in the diagram below.

The particle is travelling with a velocity of $3.0\mathrm{m}/\mathrm{s}$in a direction ${45}^{鈭�}$below the positive $x$-axis. The particle's horizontal and vertical components of velocity are then calculated.

$v_x=v\cos 鈦�{45}^{鈭�}$

$\begin{array}{r}=(3.0\mathrm{m}/\mathrm{s})\cos 鈦�{45}^{鈭�}\end{array}$

$\begin{array}{r}\\ =2.121\mathrm{m}/\mathrm{s}\end{array}$

And

$v_y=鈭�v\sin 鈦�{45}^{鈭�}$

$=鈭�(3.0\mathrm{m}/\mathrm{s})\sin 鈦�{45}^{鈭�}$

$=鈭�2.121\mathrm{m}/\mathrm{s}$

The mass $\left(m\right)$of the particle $200g$is $gtokg$

$m=200g$

$=\left(200\mathrm{g}\right)\left(\frac{1\mathrm{kg}}{1000\mathrm{kg}}\right)$

$=0.200\mathrm{kg}$

The given particle lies in the $XY$plane. Then position vector of the given particle is

$\stackrel{鈫�}{r}=\left(1.0\mathrm{m}\right)\widehat{\mathbf{i}}+\left(2.0\mathrm{m}\right)\widehat{\mathbf{j}}$

And velocity vector of the given particle is

$\stackrel{鈫�}{v}=v_x\widehat{\mathbf{i}}+v_y\widehat{\mathbf{j}}$

$=(2.121\mathrm{m}/\mathrm{s})\widehat{\mathrm{i}}+(鈭�2.121\mathrm{m}/\mathrm{s})\widehat{\mathrm{j}}$

$=(2.121\widehat{\mathrm{i}}鈭�2.121\widehat{\mathrm{j}})\mathrm{m}/\mathrm{s}$

Since angular momentum is the rotational equivalent of linear momentum in much the same way that torque is the rotational equivalent of force. Angular momentum in vector notation is given by

$\stackrel{鈫�}{L}=\stackrel{鈫�}{r}脳\stackrel{鈫�}{p}$

$=\stackrel{鈫�}{r}脳m\stackrel{鈫�}{v}$

$=m(\stackrel{鈫�}{r}脳\stackrel{鈫�}{v})$

$=\left(0.20\mathrm{kg}\right)\left|\begin{array}{ccc}\widehat{\mathbf{i}}& \widehat{\mathbf{j}}& \widehat{\mathbf{k}}\\ 1.0\mathrm{m}& 2.0\mathrm{m}& 0\\ 2.121\mathrm{m}/\mathrm{s}& 鈭�2.121\mathrm{m}/\mathrm{s}& 0\end{array}\right|$

$=\left(0.20\mathrm{kg}\right)\left[\widehat{\mathbf{i}}\right(0鈭�0)+\widehat{\mathbf{j}}(0鈭�0)+\widehat{\mathbf{k}}(1.0\mathrm{m}\left)\right(鈭�2.121\mathrm{m}/\mathrm{s})鈭�(2.0\mathrm{m}\left)\right(2.121\mathrm{m}/\mathrm{s}\left)\right]$

$\stackrel{鈫�}{L}=鈭�\left(1.273\mathrm{kg}鈰�{\mathrm{m}}^2/\mathrm{s}\right)\widehat{\mathbf{k}}$