A0.20-kg object attached to the end of a string swings in a vertical circle (radius = 80 cm). at the top of the circle the speed of the object is 4.5 m/s. what is the magnitude of the tension in the string at this position?

Tension in the string at this position: 3.1 N.

Explanation:

Convert the radius of the circle to meters:

.

What's the net force on the object?

The object is in a circular motion. As a result,

,

where

For this object,

.

The output unit of net force should be standard if the unit for mass, velocity, and radius are all standard. The net force shall always point towards the center. In this case the net force points downwards.

What are the forces on this object?

There are two forces on the object at this moment:

What's the size of the tension force?

Gravity and tension points in the same direction. The size of their resultant force is the sum of the two forces. In other words,

.

.

All three values in this question are given with two sig. fig. Round the value of to the same number of significant figures.

the electric field is a “force field” around a charged object that illustrates the direction the electric force would push an imaginary 

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.