A 20g mass is attached to a 120cm long string and moves in a horizontal circle with a constant speed of 1.5m/s . What is the angle that the string makes with a line perpendicular to the ground.

I know this is a centripetal motion problem, but I always end up with too many variables to find the angle.

Question

A 20g mass is attached to a 120cm long string and moves in a horizontal circle with a constant speed of 1.5m/s . What is the angle that the string makes with a line perpendicular to the ground.

I know this is a centripetal motion problem, but I always end up with too many variables to find the angle.

theoreo · Answer

Here's a picture and the question.

anonymous · Answer

the centripetal force has to be provided by the horizontal component of the tension in the string
and the weight of the mass has to be balanced by the vertical component of the tension
those two facts expressed as equations should then combine to give you a single equation that can be solved for the angle

theoreo · Answer

Ok so the two equations are this right?

$$F_y= F*\cos \alpha +(-m*g) = 0$$
$$F_x= F* \sin \alpha = m * a_(radial)$$

I'm not sure where to go from here though since I can't get a number for A_(radial)

anonymous · Answer

the standard formula for centripetal acceleration is v squared divided by radius