# Finding tension of a string spinning horizontally

## Homework Statement

Spin 340 gram mass at the end of a 72 cm string in a horizontal circle around head 2.5 rev/s. Calculate tension

## The Attempt at a Solution

I know tension might be equal to mass times centripetal acceleration, but I’m not sure

CWatters
Homework Helper
Gold Member
Make a free body diagram showing the forces on the mass.

PeterO
Homework Helper

## Homework Statement

Spin 340 gram mass at the end of a 72 cm string in a horizontal circle around head 2.5 rev/s. Calculate tension

## The Attempt at a Solution

I know tension might be equal to mass times centripetal acceleration, but I’m not sure
Not sure if that is what it is or not sure how to calculate it? Why not do the calculation anyway and see if the answer inspires you with any confidence.

This must be a trick question.

gneill
Mentor
This must be a trick question.
How so?

Chestermiller
Doc Al
Mentor
I know tension might be equal to mass times centripetal acceleration, but I’m not sure
Hint: Is the string horizontal?

As CWatters suggests, draw a free body diagram for the mass. Analyze horizontal and vertical forces.

CWatters
This must be a trick question.

How so?
The question is unclear and implies that the string is horizontal, which is impossible.

PeterO
Homework Helper
The question is unclear and implies that the string is horizontal.
I suppose you could do a calculation assuming the string was horizontal and IF the Tension calculates to many times the weight force, the assumption was reasonable - given the answer will be to 2 significant figures only. Otherwise the question is quite tricky, and the free-body diagram is a good, next, starting point

gneill
Mentor
The question is unclear and implies that the string is horizontal.
No, it only says that the mass moves in a horizontal circle. Students should be savvy enough to know (or discover) that the string will not be horizontal. It's a learning opportunity, not a trick.

ZapperZ
Staff Emeritus

## The Attempt at a Solution

I know tension might be equal to mass times centripetal acceleration, but I’m not sure

This is not "The attempt at a solution".

You must at least know how to start such a problem, i.e. with a free-body diagram. Can't you at least do that and show this? Otherwise, you have a bigger problem in basic mechanics than just this question.

Please note that we can only build upon what you already know! Without you describing what you already know, there's nothing to build on.

Zz.