AvSci ETEB 2024

A grinding wheel is spinning counterclockwise at a rate of 21.0 revolutions per second. When the power to the grinder is turned off, the grinding wheel slows with a constant angular acceleration and takes

70.0 s to come to a rest. What was the angular acceleration (in rad/s²)

of the grinding wheel as it came to rest if we take a counterclockwise rotation as positive?

• 0.94 rad/s²

• -0.94 rad/s²

• -0.05 rad/s²

• 0.05 rad/s²

• -1.89 rad/s²

A and B are two solid cylinders made of aluminium. Their dimensions are shown. The ratio of the rotational inertia of B to that of A about the common axis

X−X'𝑋−𝑋′

is: 

• 2

• 4

• 8

• 16

• 32

The maximum possible RPM of a Cessna 172 propeller is 2700 RPM. Determine the maximum angular velocity of the propeller. 

• 300 rad/s

• 272 rad/s

• 282 rad/s

• 2700 rad/s

Use the answer from Question Three to find the tangential velocity of the tip of the propeller blades, when at maximum RPM. The distance from the centre of the shaft to a propeller tip is 2.00 m

• 600 m/s

• 580 m/s

• 565 m/s

• 565 rad/s

• 600 rad/s

What is the angular acceleration with no-one on the merry-go round? Answer in rad/s²

What is the angular acceleration with an 18.0 kg child 1.25m away from the centre? Answer in rad/s²

Answer explanation

Reasonableness check: This should be lower than for with no-one on the merry-go-round

A ball of mass 0.22 kg, attached to a 0.50 m string is being spun anticlockwise in a vertical circle. At the instant it is directly above the centre of the circle it is making; its angular speed is 5.4 rad/s. If the string breaks at this point, with what speed will the ball fly off?

• 3 m/s

• 5 m/s

• 3 rad/s

• 2.7 m/s

What is the tension in the string (from Question Six) before it breaks?

• 10 N

• 1.0 N

• 5 N

• 2.12 N

What is the rotational inertia of the whole assembly of blades? Answer will be in kg m²

What is the kinetic energy of the assembly if it spins at 300 RPM? Answer will be in MJ.