A solid sphere, spherical shell, solid cylinder, and a cylindrical shell all have the same mass m and radius R. The same torque is applied on the rim for each of them, so that they all start to rotate about their long central axes from rest. Which object has the greatest angular speed after the same time interval

Respuesta :

Answer:

the solid sphere has the smallest moment thus angular veloicty is the largest in the system

Explanation:

One of the easiest ways to solve this exercise is by using Newton's second law for rotational motion.

          τ = I α

          α = τ / I

now let's use the rotational kinematics relations

          w = w₀ + α t

as the bodies start from rest, their angular velocity is zero w or = 0

          w = α t

we substitute

          w = [tex]\frac{\tau }{I} \ t[/tex]

the body's inertia moments are

a) solid sphere        I₁ = 2/5 m r²

b) spherical shell    I₂ = ⅔ me r²

c) solid cylinder      I₃ = ½ m r²

d) cylindrical shell  I₄ = m r²

Let's analyze the expression for angular velocity, all bodies apply the same torque and it is measured in time, therefore the angular velocity is inversely proportional to the moment of inertia.

When examining the moment of inertia the largest is the moment of inertia of the cylindrical shell

the one with the lowest initial moment

we take all the values ​​to fractions with the same denominator

           I₁ = 2/5 6/6 m r² = 12/30 m r²

           I₂ = ⅔ 10/10 m r² = 20/30 m r²

           I₃ = ½ 15/15 m r² = 15/30 m r²

therefore the order of the moments of inertia is

           I₁ <I₃ <I₂ <I₄

Therefore, since the solid sphere has the smallest moment thus angular veloicty is the largest in the system