Net force and position of objects in space

[dayspassingby]

Homework Statement

Q1) t = 493 s after midnight, a spacecraft of mass 2800 kg is located at position <9 × 105, 8 × 105, -3 × 105> m, and at that time an asteroid whose mass is 9 × 1015 kg is located at position <6 × 105, -9 × 105, -14 × 105 > m. There are no other objects nearby.

a) Calculate the (vector) force acting on the spacecraft.

b) At 493 s the spacecraft's momentum was , and at the later time 500 s its momentum was . Calculate the (vector) change of momentum .

Q2) A star of mass 3 × 1030 kg is located at <8 × 1012, 5 × 1012, 0> m. A planet of mass 6 × 1024 kg is located at <4 × 1012, 9 × 1012, 0> m and is moving with a velocity of <0.6 × 104, 1.1 × 104, 0> m/s.

a) During a time interval of 1 × 106 seconds, what is the change in the planet's velocity?\

b) During this time interval of 1 × 106 seconds, what is the change in the planet's position?

Q3) A planet of mass 7 × 1024 kg is at location <-2 × 1011, 5 × 1011, 0> m. A star of mass 4 × 1030 kg is at location <2 × 1011, -2 × 1011, 0> m. What is the force exerted on the planet by the star? (It will probably be helpful to draw a diagram, including the relevant vectors.)

Relevant Equations

Fnet = Gm1m2 / d^2 *unit vector

Q1a)
- My current wrong answer is <-5.9e7, -3.3e8, -2.17e8> I used the Fnet = Gm1m2 / d^2 <unit vector> But i keep getting a dif answer each time

Q2a) - I thought i could find net force and then divide it by the mass, and multiply it by the time interval. However I got the answer <-4.5, 4.5, 0> which is wrong

Q3)
I subtracted the planet by the star vector. Then, I used Gm1m2 / d^2 times the unit vector. But that just gave me <-1.43e21, 2.495e21, 0> Which is wrong

 

[haruspex]

It is preferred that you post each problem as a separate thread.

In each case, please post all your working.
In 2a, will the force be sufficiently constant over that period to treat it as such?

 

[BvU]

Hello @dayspassingby

$\qquad$ !​

Please don't give the numerical answers you get but post the steps you take to get them.
And have pity on us: you don't mean 9135 kg when you write 9 x 1015 kg. So write 9 x 10¹⁵ kg using the superscript button

or learn a little $\TeX$ with the

to get $9\times 10^{15}$ kg

https://www.physicsforums.com/threads/homework-help-guidelines-for-students-and-helpers.686781/

keep getting a dif answer each time

Tip: estimate the answer (coarsely) before using a calculator. In this case, do you really expect forces to the tune of $10^8$ N ? $\$