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Hi Guys,

I think I've done the question below correctly but my result doesn't jive with a couple others I have found online for the same problem (answers of 160kg and 170kg). I want to insure I get full marks (of course) while simultaneously making sure I am understanding the concepts correctly. I'm wondering if I'm doing this right, I think the variance in answers must be rounding errors, maybe on my part or maybe on the part of the other individuals...

The question;

"A 7600-kg space probe is travelling through space at 120 m/s. Mission control determines that a change in course of 30.0° is necessary and, by electronic communication, instructs the probe to fire rockets perpendicular to its present direction of motion. If the escaping gas leaves the crafts rockets at an average speed of 3200 m/s, what mass of gas should be expelled?"

My Answer and logic,

(sorry for the crude diagram)

...................^

................../|

................./ |

.............. /60|

............./.....|

..........C/......|

........../........| A

....... /..........|

..... /............|

... /..............|

../30...... 90...|

/--------------->

......B...........

So I make my vector triangle, and attain B.

B = 7600kg * 120m/s = 912,000kg *m/s = 9.12 * 10^5 kg*m/s

now I use law of sines to get side A.

A = (sin 30.0) * (9.12 * 10^5 kg*m/s)/(sin 60.0) = 526543.45 = 5.26 * 10^5kg*m/s

So now I have A = 5.26 * 10kg*m/s and I devide by 3200m/s to get 164.38 = 1.64 * 10^2kg or 164kg.

So my final answer is 164kg which apparently doesn't agree with some similar question/answers I've seen for honors physics on the net..

Any ideas?

I think I've done the question below correctly but my result doesn't jive with a couple others I have found online for the same problem (answers of 160kg and 170kg). I want to insure I get full marks (of course) while simultaneously making sure I am understanding the concepts correctly. I'm wondering if I'm doing this right, I think the variance in answers must be rounding errors, maybe on my part or maybe on the part of the other individuals...

The question;

"A 7600-kg space probe is travelling through space at 120 m/s. Mission control determines that a change in course of 30.0° is necessary and, by electronic communication, instructs the probe to fire rockets perpendicular to its present direction of motion. If the escaping gas leaves the crafts rockets at an average speed of 3200 m/s, what mass of gas should be expelled?"

My Answer and logic,

(sorry for the crude diagram)

...................^

................../|

................./ |

.............. /60|

............./.....|

..........C/......|

........../........| A

....... /..........|

..... /............|

... /..............|

../30...... 90...|

/--------------->

......B...........

So I make my vector triangle, and attain B.

B = 7600kg * 120m/s = 912,000kg *m/s = 9.12 * 10^5 kg*m/s

now I use law of sines to get side A.

A = (sin 30.0) * (9.12 * 10^5 kg*m/s)/(sin 60.0) = 526543.45 = 5.26 * 10^5kg*m/s

So now I have A = 5.26 * 10kg*m/s and I devide by 3200m/s to get 164.38 = 1.64 * 10^2kg or 164kg.

So my final answer is 164kg which apparently doesn't agree with some similar question/answers I've seen for honors physics on the net..

Any ideas?

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