Section I: Multiple Choice 1. A disc has a radius of 5 cm. If the disc rotates about its 5. A uniform 10-m ladder with a mass of 20 kg rests central axis at an angular speed of 8 rev/s, what is the against a wall such that it makes a 50 angle with the linear speed of a point on the rim of the disc? ground. If the friction between the ladder and the wall (A) 0.4 m/s is negligible, what is the force the ladder exerts on the (B) 2.5 m/s wall? (C) 3.9 m/s (A) 82 N (D) 50 m/s (B) 98 N (C) 164 N 2. An object, initially at rest, begins spinning under a (D) 196 N constant angular acceleration. In 15 s, it completes an angular displacement of 90 rad. What is the magnitude 6. An object spins with an angular velocity @. If the of the angular acceleration it experiences? object's rotational inertia increases by a factor of 4, (A) 0.4 rad/s without the application of external torque, what will be (B) 0.8 rad/s the object's new angular velocity? C) 6 rad/s A) w/4 12 rad/s B) W/2 (C) 20 D) 40 3. A wheel initially rotating at 12 rad/s decelerates uniformly to rest in 0.4 s. If the wheel has a rotational inertia of 0.5 kg.m?, what is the magnitude of the torque 7. A child with a mass of 25 kg is standing at the edge of causing this deceleration? a 2.0 m radius merry-go-round, and they are rotating without friction at 20 rpm. The child then moves toward (A) 1.5 N.m the center of the merry-go-round. The merry-go-round (B) 15 N.m has a rotational inertia of 1200 kg-m', and the rotational C) 30 N.m inertia of the child is I = mr?, where r is her distance (D) 38 N.m from the axis of rotation. What is the new angular velocity when she is 0.5 m from the center of the 4. A grinding wheel with a radius of 12 cm is being used merry-go-round? to sharpen a knife. The side of the knife is pressed (A) 2.03 rad/s perpendicularly into the wheel's surface with a force (B) 2.09 rad/s of 16 N. The coefficient of kinetic friction between (C) 2.15 rad/s the knife and the wheel is 0.28. What is the torque the (D) 2.25 rad/s grinding wheel's motor must supply to maintain its rotation rate of 50 rad/s? (A) 0.50 N.m (B) 0.72 N.m (C) 4.5 N.m D) 54 N.m