10 minutes maximum! Can you do it in 5? 
1. Which one of the following best describes a 'centripetal' force?
 A. A force acting against motion that produces circular motion.
 B. A force acting at right angles to the velocity of a body, that produces circular motion.
 C. A force caused by circular motion, acting at right angles to the velocity and pushing a body away from the centre of the circle.
 D. A force caused by circular motion, making the speed of a body change.


2. Which of the following best describes the changes to speed and velocity (if any) as an object moves in orbit, such as a moon around a planet?

Speed 
Velocity 
A 
constant 
constant 
B 
changes^{} 
constant 
C 
constant 
changes^{} 
D 
changes^{} 
changes^{} 


3. A child is riding on a roundabout ride. After 2 seconds, the child has completed half a rotation.
What is the angular velocity of this roundabout? 

 A. 0 rad s^{1}
 B. ¼π rad s^{1}
 C. ½π rad s^{1}
 D. π rad s^{1}



4. What force keeps an electron in orbit around a nucleus?
 A. An electrical force.
 B. A gravitational force.
 C. A centrifugal force.
 D. Frictional forces.
 
57. The diagram below shows a 4 kg mass being whirled round in a horizontal orbit at the end of a 2m long rope. The velocity of the mass is constant at 10 ms^{1}.


5. What is the value of the angular velocity?
 A. 10 ms^{1}.
 B. 20 ms^{1}
 C. 10 rad s^{1}
 D. 5 rad s^{1}


6. What is the value of the centripetal acceleration?
 A. 20 ms^{2}
 B. 10 ms^{2}
 C. 5 ms^{2}
 D. 50 ms^{2}


7. What is the tension in the rope keeping the mass moving in a circle?
 A. 200 N
 B. 20 N
 C. 100 N
 D. 50 N
 
810. A fan used to cool a room rotates at a frequency of 10 Hz._{}
The length of each blade is 0.5 m from the centre of rotation. 

8. What is the period of the fan?
 A. 2π s
 B. π s
 C. 10 s
 D. 0.1 s


9. What distance has been travelled, in meters, by the tip of the fan blade in this time period?
 
10. The fan slows down to a frequency of 1 Hz. What is the centripetal acceleration on the tips of the blades at this frequency?
 A. 2π^{2} ms^{2}
 B. 2π ms^{2}
 C. 4π ms^{2}
 D. 4π^{2} ms^{2}
 
