# Tension in string

#### John78

1. Homework Statement

Calculate the tension in a 5 m string attached to a 4 kg bob that is moving in horizontal circles of 0.6 m radius.

2. Homework Equations

3. The Attempt at a Solution

α= tan-1 0.6/5
= 7 degree

T cos α = m*g

T= m*g/cosα

T=4*9.8/0.12

T=326.6 N

I just want to check whether my working is correct or not.

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#### PhanthomJay

Homework Helper
Gold Member
Your equations are almost correct, however, if the angle α is 7 degrees, then cos α = cos 7 = ? But your calc for that angle is not right. It is not the tan function per your attempt................

#### John78

so am I right in my calculations

α= sin 0.6/5
= 7 degree = 0.121869343

T cos α = m*g

T= m*g/cosα

T=4*9.8/0.121869343

T=321.65N

#### PhanthomJay

Homework Helper
Gold Member
so am I right in my calculations

α= sin^-1 0.6/5 = sin^-1 0.12
α = 6.9 degrees

T cos α = m*g

T= m*g/cosα
yes
T=4*9.8/0.121869343
No, the cosine of 6.9 degrees is not 0.121869343

#### John78

cos 6.9 = 0.992757341

Am I right?

Homework Helper
Gold Member

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