Unreasonable Results A gymnast doing a forward flip lands on the mat and exerts a 500- N ⋅ m torque to slow and then reverse her angular velocity . Her initial angular velocity is 10.0 rad/s, and her moment of inertia is 0.050 kg ⋅ m 2 . (a) What time is required for her to exactly reverse her spin? (b) What is unreasonable about the result? (c) Which premises are unreasonable or inconsistent?
Unreasonable Results A gymnast doing a forward flip lands on the mat and exerts a 500- N ⋅ m torque to slow and then reverse her angular velocity . Her initial angular velocity is 10.0 rad/s, and her moment of inertia is 0.050 kg ⋅ m 2 . (a) What time is required for her to exactly reverse her spin? (b) What is unreasonable about the result? (c) Which premises are unreasonable or inconsistent?
A gymnast doing a forward flip lands on the mat and exerts a 500-
N
⋅
m
torque to slow and then reverse her angular velocity. Her initial angular velocity is 10.0 rad/s, and her moment of inertia is
0.050
kg
⋅
m
2
. (a) What time is required for her to exactly reverse her spin? (b) What is unreasonable about the result? (c) Which premises are unreasonable or inconsistent?
Definition Definition Rate of change of angular velocity. Angular acceleration indicates how fast the angular velocity changes over time. It is a vector quantity and has both magnitude and direction. Magnitude is represented by the length of the vector and direction is represented by the right-hand thumb rule. An angular acceleration vector will be always perpendicular to the plane of rotation. Angular acceleration is generally denoted by the Greek letter α and its SI unit is rad/s 2 .
2.62 Collision. The engineer of a passenger train traveling at
25.0 m/s sights a freight train whose caboose is 200 m ahead on the
same track (Fig. P2.62). The freight train is traveling at 15.0 m/s in the
same direction as the passenger train. The engineer of the passenger
train immediately applies the brakes, causing a constant acceleration
of 0.100 m/s² in a direction opposite to the train's velocity, while the
freight train continues with constant speed. Take x = 0 at the location
of the front of the passenger train when the engineer applies the brakes.
(a) Will the cows nearby witness a collision? (b) If so, where will it take
place? (c) On a single graph, sketch the positions of the front of the pas-
senger train and the back of the freight train.
Can I get help with how to calculate total displacement? The answer is 78.3x-4.8y
2.70 Egg Drop. You are on the Figure P2.70
roof of the physics building, 46.0 m
above the ground (Fig. P2.70). Your
physics professor, who is 1.80 m tall,
is walking alongside the building at
a constant speed of 1.20 m/s. If you
wish to drop an egg on your profes-
sor's head, where should the profes-
sor be when you release the egg?
Assume that the egg is in free fall.
2.71 CALC The acceleration
of a particle is given by ax(t) =
-2.00 m/s² +(3.00 m/s³)t. (a)
Find the initial velocity Vox such that
v = 1.20 m/s
1.80 m
46.0 m
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