24. a 27-kg ball is tied to one end of a massless string of length 1.3 m. the other end of the string is tied to a nail in the center of a table. the
ball is set into uniform circular motion around the nail, and it completes one revolution every 5.2 seconds. what is the tension in the
string?
51n
44n
71n
30 n

51 N

Explanation:

The circumference of the circular path is:

C = 2πr

C = 2π (1.3 m)

C = 8.17 m

The ball travels 1 circumference in 5.2 seconds, so its speed is:

v = C / t

v = 8.17 m / 5.2 s

v = 1.57 m/s

Sum of the forces on the ball in the radial direction:

∑F = ma

T = m v² / r

T = (27 kg) (1.57 m/s)² / (1.3 m)

T = 51 N

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

because if the tool that you are using is not balanced it there would be false mass.