How Do You Calculate Tension in a String When Accelerating Upwards?

[Kajayacht]

Homework Statement

A sphere of mass of 1.55 kg is accelerated upwards by a string to which the sphere is attached. Its speed increases from 2.21 m/s to 5.30 m/s in a time of 1.62 s. Calculate the tension in the string, assuming that the tension remains constant during that time.

Homework Equations

a = (delta)V/(delta)t
T = m(g + a)
m = wg

The Attempt at a Solution

a = (5.30 - 2.21)/1.62 = 1.91m/s^2
m = 1.55*9.8 = 15.19
T = 15.19(9.8 + 1.91) = 177.87 N

 

[Doc Al]

Homework Equations

a = (delta)V/(delta)t
T = m(g + a)

Good.

m = wg

Not good. You're thinking of w = mg.

The Attempt at a Solution

a = (5.30 - 2.21)/1.62 = 1.91m/s^2

Good.

m = 1.55*9.8 = 15.19

Not good. m = 1.55 kg (it's given!).