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A spacecraft on its way to Mars has small rocket engines mounted on its hull; one on its left surface and one on its back surface. At a certain time, both engines turn on. The one on the left gives the spacecraft an acceleration component in the [tex]x[/tex] direction of [tex]a_x=5.10 \, \text{m/s}^2[/tex], while the one on the back gives an acceleration component in the [tex]y[/tex] direction of [tex]a_y=7.30 \, \text{m/s}^2[/tex]. The engines turn off after firing for [tex]630 \, \text{s}[/tex], at which point the spacecraft has velocity components of [tex]v_x=3740 \, \text{m/s}[/tex] and [tex]v_y=4472 \, \text{m/s}[/tex].

1. What was the magnitude and the direction of the spacecraft's initial velocity before the engines were turned on? Express the magnitude as [tex]\text{m/s}[/tex] and the direction as an angle measured counterclockwise from the [tex]+x[/tex] axis.
- Magnitude: [tex]\square \, \text{m/s}[/tex]
- Direction: [tex]\square \, ^{\circ}[/tex]

2. Draw a diagram of the final velocity vector based on its components. What trigonometric relation will allow you to find the direction? [tex]^{\circ}[/tex] counterclockwise from the [tex]+x[/tex] axis.


Sagot :

To solve the problem and find the magnitude and direction of the spacecraft's initial velocity before the engines were turned on, follow these steps:

1. Extract Given Data:
- Acceleration in the [tex]\( x \)[/tex]-direction, [tex]\( a_x = 5.10 \, \text{m/s}^2 \)[/tex].
- Acceleration in the [tex]\( y \)[/tex]-direction, [tex]\( a_y = 7.30 \, \text{m/s}^2 \)[/tex].
- Time the engines were on, [tex]\( t = 630 \, \text{s} \)[/tex].
- Final velocity in the [tex]\( x \)[/tex]-direction, [tex]\( v_{x_{\text{final}}} = 3740 \, \text{m/s} \)[/tex].
- Final velocity in the [tex]\( y \)[/tex]-direction, [tex]\( v_{y_{\text{final}}} = 4472 \, \text{m/s} \)[/tex].

2. Calculate Initial Velocities:
- For the [tex]\( x \)[/tex]-direction:
[tex]\[ v_{x_{\text{initial}}} = v_{x_{\text{final}}} - a_x \times t \][/tex]
Substituting the given values:
[tex]\[ v_{x_{\text{initial}}} = 3740 \, \text{m/s} - (5.10 \, \text{m/s}^2 \times 630 \, \text{s}) = 527 \, \text{m/s} \][/tex]

- For the [tex]\( y \)[/tex]-direction:
[tex]\[ v_{y_{\text{initial}}} = v_{y_{\text{final}}} - a_y \times t \][/tex]
Substituting the given values:
[tex]\[ v_{y_{\text{initial}}} = 4472 \, \text{m/s} - (7.30 \, \text{m/s}^2 \times 630 \, \text{s}) = -127 \, \text{m/s} \][/tex]

3. Calculate the Magnitude of the Initial Velocity:
The magnitude of the initial velocity [tex]\( v_{\text{initial}} \)[/tex] can be found using the Pythagorean theorem:
[tex]\[ v_{\text{initial}} = \sqrt{(v_{x_{\text{initial}}})^2 + (v_{y_{\text{initial}}})^2} \][/tex]
Substituting the values:
[tex]\[ v_{\text{initial}} = \sqrt{(527)^2 + (-127)^2} \approx 542.09 \, \text{m/s} \][/tex]

4. Calculate the Direction of the Initial Velocity:
The direction of the initial velocity θ, measured counterclockwise from the [tex]\( +x \)[/tex]-axis, can be found using the inverse tangent function:
[tex]\[ \theta = \tan^{-2} \left( \frac{v_{y_{\text{initial}}}}{v_{x_{\text{initial}}}} \right) \][/tex]
Substituting the values:
[tex]\[ \theta = \tan^{-2} \left( \frac{-127}{527} \right) \approx -13.55^\circ \][/tex]
Since the arctangent function gives an angle with respect to the [tex]\( x \)[/tex]-axis, and the result is negative, this angle indicates a direction below the positive [tex]\( x \)[/tex]-axis (clockwise). However, when describing direction as counterclockwise from the [tex]\( +x \)[/tex]-axis, use the negative sign as is to maintain convention.

Thus, the magnitude of the spacecraft's initial velocity is approximately [tex]\( 542.09 \, \text{m/s} \)[/tex] and the direction is [tex]\( -13.55^\circ \)[/tex] counterclockwise from the [tex]\( +x \)[/tex]-axis.
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