Need answers to 78910 6 A fan rotating with an initial angul

6. A fan rotating with an initial angular velocity of 1000 revimin is switched off. In 2 seconda, the anusa velocity decreases to 200 rev/min. Assuming the angular acceleration is constant, how many revolutions does the blade undergo during this time? A) 10 B) 20 C) 100 D) 125 E) 1200 7. A wrench is used to tighten a nut as shown in the figure. A 12-N force is applied 7.0 cm from the axis of rotation. The magnitude of te torque due to the applied force 7.0 em A) 0.58 N m B) 0.84 Nm C) 1.71 N m D) 14N m E) 58 N m 8. A uniform 240-g meter stick can be balanced by a 240-g weight placed at the 100-cm mark if the fulcrum is placed at the point marked: A) 75 cm B) 60 cm C) 50 cm D) 40 cm E) 80 cm 9. A meter stick is pivoted at the 0.50-m line. A 3.0-kg object is hung from the 0.15-m line. To balance the meter stick, a 5.0-kg object is hung at: A) 0.06-m line B) 0.24-m line C) 0.56-m line D) 0.71-m line E) A 5.0-kg object cannot be placed anywhere on the meter stick to result in equilibrium in this system 10. A spinning skater draws in her outstretched arms thereby reducing her moment of inertia by a factor of 2. The ratio of her final kinetic energy to her initial kinetic energy is: A) 0.5 B) 1 C) 2 D) 4 E) 16

Solution

7. torque = perpandicular distance x force = 0.07 x 12 = 0.84 Nm

8. let x is point

then x must be between 50 cm and 100 cm mark to balance

now (x-50)240 = (100-x)240

=> x = 75 cm

9) 3(0.5 - 0.15) = 5(x-0.5)

=> 3*0.35/5 = x - 0.5 => x = 0.71 m

10) I₂/I₁ = 0.5

K₂/K₁ = I₁/I₂ = 2