Question

A 0.1 kg yo-yo is initially hanging at rest at the end of its string. Then the tension force in the string is adjusted to 0.6 N pulling upward.
Which one of the following describes how the yo-yo will move once the string’s force is adjusted?
A.) The yo-yo will accelerate upward
B.) The yo-yo will accelerate downward
C.) The yo-yo will move upward at a constant velocity
D.) The yo-yo will move downward at a constant velocity

Answer 1

Hint: Firstly, calculate the gravitational force exerted on the yo-yo, thereafter compare the tension force and the gravitational force, to determine in which direction yo-yo will move or accelerate.

Complete step by step answer:

Given that the mass of the yo-yo = 0.1 kg
and the tension force = 0.6 N
The gravitational force acting on the yo-yo is given by,

${{F}_{g}}=W=mg$

Where,

${{F}_{g}}$ = gravitational force
$W$ = weight
$m$ = mass
$g$ = acceleration due to gravity $\left( g=9.8m/{{s}^{2}} \right)$

$\Rightarrow {{F}_{g}}=\left( 0.1\times 9.8 \right)N$

$\Rightarrow {{F}_{g}}=0.98N$acting downward.

Now it is given that the tension force $T=0.6N$ is acting in an upward direction.

So, we can easily compare that the ${{F}_{g}}>T$ and ${{F}_{g}}$ is acting in downward direction.

Therefore, the yo-yo will accelerate in a downward direction.

Hence, the correct option is B, i.e., The yo-yo will accelerate downward.

Note: Students should keep in mind that the weight of an object is the gravitational force applied in downward direction. Students also need to know that the unbalanced force is the cause of motion. So that they can easily compare the forces exerted on a mechanical system and determine the direction of motion.