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A horizontal 652 N merry-go-round of radius 1.37 m is started from rest by a constant horizontal force of 77 N applied tangentially to the merry-go-round. Find the kinetic energy of the merry-go-round after 3.93 s. The acceleration of gravity is 9.8 m/s². Assume the merry-go-round is a solid cylinder. Answer in units of J.

Answer :

The kinetic energy of the merry-go-round after 3.93 seconds is approximately 135.7 J.

Here's the approach:

Calculate the moment of inertia (I) of the merry-go-round.

We can use the formula for the moment of inertia of a solid cylinder:

I = (1/2) × M × [tex]R^2[/tex]

where:

I is the moment of inertia (kg m²)

M is the mass of the merry-go-round (kg)

R is the radius of the merry-go-round (m)

First, we need to convert the weight of the merry-go-round from Newtons (N) to mass (kg) using the following conversion:

M = weight / g

where:

M is the mass (kg)

weight is the weight of the merry-go-round (N)

g is the acceleration due to gravity (9.8 m/s²)

Therefore:

M = 652 N / 9.8 m/s² ≈ 66.43 kg

Now, we can calculate the moment of inertia:

I = (1/2) × 66.43 kg × (1.37 m)² ≈ 58.49 kg m²

Calculate the angular acceleration (α) of the merry-go-round.

We can use Newton's second law of rotational motion, which states:

τ = I × α

where:

τ is the torque (N m)

I is the moment of inertia (kg m²)

α is the angular acceleration (rad/s²)

In this case, the torque is equal to the applied tangential force (F_t) multiplied by the radius (R):

τ = F_t × R

Therefore:

α = (F_t × R) / I

α = (77 N × 1.37 m) / 58.49 kg m² ≈ 1.91 rad/s²

Calculate the angular velocity (ω) of the merry-go-round after 3.93 seconds.

We can use the following kinematic equation for rotational motion:

ω = α × t

where:

ω is the angular velocity (rad/s)

α is the angular acceleration (rad/s²)

t is the time (s)

Therefore:

ω = 1.91 rad/s² × 3.93 s ≈ 7.51 rad/s

Calculate the kinetic energy (KE) of the merry-go-round.

We can use the formula for the kinetic energy of a rotating object:

KE = (1/2) × I × ω^2

where:

KE is the kinetic energy (J)

I is the moment of inertia (kg m²)

ω is the angular velocity (rad/s)

Therefore:

KE = (1/2) × 58.49 kg m² × (7.51 rad/s)² ≈ 135.7 J

Therefore, the kinetic energy of the merry-go-round after 3.93 seconds is approximately 135.7 J.

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