first question:(adsbygoogle = window.adsbygoogle || []).push({});

1. The problem statement, all variables and given/known data

A 5.5e4 kg space probe is traveling at a speed of 11000 m/s through deep space. Retrorockets are fired along the line of motion to reduce the probe's speed. The retrorockets generate a force of 4.5e5 N over a distance of 2500 km. What is the final speed of the probe?

2. Relevant equations

W=FDcos(theta)

KE=1/2mv^2

PE=mgh

3. The attempt at a solution

(4.5e5N)(2500000m)cos0=1.125e12

(5.5e4)(9.8)(11000)=5929000000

1.125e12-5929000000=1.11907e12

I don't have any clue how to do this problem... i've attempted many times and got several different answers that are all wrong including 6386269.138, 6386269138, 9824.33, 4947.530329, 6396.021491, 4603.978509, and 6379.144998.

second question:

1. The problem statement, all variables and given/known data

A 47.0 g golf ball is driven from the tee with an initial speed of 50.0 m/s and rises to a height of 23.6 m.

What is its speed when it is 6.0 m below its highest point?

2. Relevant equations

W=FDcos(theta)

KE=1/2mv^2

PE=mgh

3. The attempt at a solution

KE=47.87984

47.87984-6=41.87984

I figured there would need to be more work involved than just that but I dont even know where to begin.

third question:

1. The problem statement, all variables and given/known data

A 54.5 kg. skateboarder starts out with a speed of 1.70 m/s. He does +80.0 J of work on himself by pushing with his feet against the ground. In addition, friction does -265 J of work on him. In both cases, the forces doing the work are nonconservative. The final speed of the skateboarder is 6.10 m/s.

(a) Calculate the change (changePE = PEf - PE0) in the gravitational potential energy.

(b) How much has the vertical height of the skater changed?

2. Relevant equations

W=FDcos(theta)

KE=1/2mv^2

PE=mgh

3. The attempt at a solution

-265-80=-345

I tried to attempt b and got 11295.9455 ans 2 as my answers but I don't remember exactly what i did to get them.

Sorry about posting 3 questions! I know that's a lot for one post. I have this online homework assignment due by 11:59 pm and I currently have a 17.84/20. I'm very frusterated with these three problems and no one in my class can get them either. I was hoping someone here could help. Thank you all so much!!! Your help is greatly appreciated.

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# Homework Help: Questions on Conservation of Enery

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