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A uniform circular disc of radius 50 cm50 \text{ cm} at rest is free to turn about an axis that is perpendicular to its plane and passes through its centre. It is subjected to a torque that produces a constant angular acceleration of 2.0 rad/s22.0 \text{ rad/s}^2. Its net acceleration in m/s2\text{m/s}^2 at the end of 2.0 s2.0 \text{ s} is approximately:

A

7

B

6

C

3

D

8

Step-by-Step Solution

Given: Radius of the disc, r=50 cm=0.5 mr = 50 \text{ cm} = 0.5 \text{ m} Initial angular velocity, ω0=0\omega_0 = 0 (since it is at rest) Angular acceleration, α=2.0 rad/s2\alpha = 2.0 \text{ rad/s}^2 Time, t=2.0 st = 2.0 \text{ s}

Angular velocity at t=2.0 st = 2.0 \text{ s} is given by the first equation of rotational kinematics: ω=ω0+αt\omega = \omega_0 + \alpha t ω=0+(2.0 rad/s2)×(2.0 s)=4.0 rad/s\omega = 0 + (2.0 \text{ rad/s}^2) \times (2.0 \text{ s}) = 4.0 \text{ rad/s}

The net linear acceleration of a particle on the rim of the disc is the vector sum of its tangential acceleration (ata_t) and centripetal acceleration (aca_c).

Tangential acceleration: at=rα=0.5 m×2.0 rad/s2=1.0 m/s2a_t = r\alpha = 0.5 \text{ m} \times 2.0 \text{ rad/s}^2 = 1.0 \text{ m/s}^2

Centripetal (radial) acceleration: ac=rω2=0.5 m×(4.0 rad/s)2=0.5×16.0=8.0 m/s2a_c = r\omega^2 = 0.5 \text{ m} \times (4.0 \text{ rad/s})^2 = 0.5 \times 16.0 = 8.0 \text{ m/s}^2

Since ata_t and aca_c are perpendicular to each other, the magnitude of the net acceleration is: a=at2+ac2a = \sqrt{a_t^2 + a_c^2} a=(1.0)2+(8.0)2=1+64=658.06 m/s2a = \sqrt{(1.0)^2 + (8.0)^2} = \sqrt{1 + 64} = \sqrt{65} \approx 8.06 \text{ m/s}^2

Therefore, the net acceleration is approximately 8 m/s28 \text{ m/s}^2.

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