Kinematics Question

[MedPR]

---

Members do not see this ad.

If the tension in a rope pulling a 150kg block in a straight line is 750N, what will be the velocity of the block after it has been pulled 200meters, if the horizontal surface it traverses has a coefficient of kinetic friction of 0.4?

A. 0.2m/s
B. 5m/s
C. 21m/s
D. 100m/s

This is a pretty straightforward kinematics/freebody diagram type problem, except for one thing. The answer is based on the assumption that initial velocity is 0 (The answer is C). The problem doesn't say anything about initial velocity being 0. I made the assumption because in most cases initial velocity is 0 unless explicitly stated otherwise.. Is there a way to solve this without setting vo to 0?

Thanks

 

[milski]

The answer will depend on Vo, so you have to assume something about it. With nothing else said, 0 is probably the most reasonable assumption. At least I will have much harder time justifying why I started with 15.04 m/s.

 

[Temperature101]

I got 20m/s...How they got 21 m/s?

Edit...It's 21 using 9.8m/s^2...I was using 10m/s^2 for g.

 

[MedPR]

I got 20m/s...How they got 21 m/s?

Edit...I use g = 10m/s^2...that might be the reason

20 is close enough 😀

 

[411309]

I don't think theres a way you can solve this problem without knowning the initial velocity is zero. They give you a lot of details but dont tell you it starts from rest? lol, ironic, I get what you're saying, it would be a super easy problem if they just included that. I just assumed it started from rest since theres no other way i know how to solve that problem.

 

[MedPR]

I don't think theres a way you can solve this problem without knowning the initial velocity is zero. They give you a lot of details but dont tell you it starts from rest? lol, ironic, I get what you're saying, it would be a super easy problem if they just included that. I just assumed it started from rest since theres no other way i know how to solve that problem.

Yea I did too, but only after I spent way too much time trying to figure it out another way. I kept coming back to "I can solve this if vo is 0.. but it's not" Then I finally gave in and it worked out. Not something I want to do on the real thing.

 

[milski]

Yea I did too, but only after I spent way too much time trying to figure it out another way. I kept coming back to "I can solve this if vo is 0.. but it's not" Then I finally gave in and it worked out. Not something I want to do on the real thing.

If you're not sure, solve it with Vo instead of a specific number. If Vo cancels, you did not need it. If it's part of your final answer, you do need it and if it's not given you have to come up with some reasonable assumption.