Why Does a Skydiver's Acceleration Differ from Calculations?

[holly]

Well, you'd think I could understand these problems by now, but...

Q. A falling skydiver of mass 100 kg experiences 500-N air resistance. The accleration of the skydiver is: a) More than .5g b).2g c).4g d).5g.

The prof gave the answer as .2g, but I get .5g by this: a=F/m. I put in 500N for F, and 1000N for his mass. Am I doing it backwards? A difficulty is that the professor will purposefully give wrong answers to us in order to "make us think," but we never know which are the wrong ones and which are right because we are just now learning this...makes it very hard for me to progress...plus I'm dumb I think.

Thanking you for any help!

 

[ShawnD]

Originally posted by holly
Well, you'd think I could understand these problems by now, but...

Q. A falling skydiver of mass 100 kg experiences 500-N air resistance. The accleration of the skydiver is: a) More than .5g b).2g c).4g d).5g.

The prof gave the answer as .2g, but I get .5g by this: a=F/m. I put in 500N for F, and 1000N for his mass.

Draw a FBD.

981N pushing down. 500N pushing up. Total of 481 pushing down.

$$a = \frac{F}{m}$$

$$a = \frac{481}{100}$$

a = 4.81

g = 4.81/9.81
g = 0.49

Your prof is a moron.

 

[M98Ranger]

It sounds like you are on the right track with your understanding of the problem. The equation a = F/m is correct, and if you plug in the values of 500N for F and 100 kg for m, you should get an acceleration of .5g.

However, it is possible that the professor may have rounded the answer to .2g for simplicity. It is also possible that there is some other factor at play that you may not be aware of yet.

In any case, it can be frustrating when you feel like you are not understanding a concept, especially when the professor intentionally gives wrong answers. My advice would be to seek clarification from the professor or a teaching assistant and ask for more practice problems to solidify your understanding. Don't be too hard on yourself for not understanding right away - learning takes time and practice. Keep at it and you will get there!