When a toy car is rapidly scooted across the floor, it stores energy in a flywhe
ID: 1432353 • Letter: W
Question
When a toy car is rapidly scooted across the floor, it stores energy in a flywheel. The car has a mass of 0.187 kg , and its flywheel has a moment of inertia of 4.04×105 kgm2 . The car has a length of 13.6 cm . An advertisement claims that the car can travel at a scale speed of up to 700 km/h . The scale speed is the speed of the toy car multiplied by the ratio of the length of an actual car to the length of the toy. Assume a that the length of a real car is 2.90 m . A)For a scale speed of 700 km/h , what is the actual translational speed of the car? B)If all the kinetic energy that is initially in the flywheel is converted to the translational kinetic energy of the toy, how much energy is originally stored in the flywheel? C)What initial angular velocity of the flywheel was needed to store the amount of energy calculated in part B?
Explanation / Answer
700 km/h = 434.95 mi / hr
No car has ever gone that fast!
290cm / 13.6 cm= 21.32 times the length of a real car
the actual translational speed of the car
= 700 km/h (1/21.32) = 32.83 km/h
32.83km/h =9.11 meters per second
use this value of v for the next part
b) linear KE = rotational KE
(1/2)mv^2
= rotational KE 1/2*0.187*9.11^2
= 7.75 (in Joules)
c)Once you get a number for part b) use
rotational KE = (1/2) I w^2
rotational KE = 1/2*4.04×105
and solve for
w, the angular velocity ,
=2.02*10^-5 (radians per second)
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