Concept Development Practice Page
9-1
Circular Motion
1. Most energy of train systems is used in starting and stopping. The rotating train platform design
saves energy, for people can board or leave a train while the train is still moving. Study the sketch
and convince yourself
that this is true. The small circular platform in the middle is stationary, and
is connected to a stationary stairway.
a. If there is to be no relative motion between the train and the edge of the platform, how fast
must the train move compared to the rim speed of the rotating platform?
b. Why is the stairway located at the center of the platform?
2. The design below shows a train that makes round trips from Station A to Station B in a
continuous loop.
a. How is the size of the round platform and train speed related to the amount of time that
passengers have for boarding?
b. Why would this rotating platform be impractical for high-speed trains?
Conceptual PHYSICS

Which type of wave can travel without a medium

For problems 1-3, consider a simple dc brush motor with a permanent magnet stator. with an an consider a simple dc brush motor with a permanent magnet ae supply voltage of 100 v, the no-load speed of the motor is 1000 rpm. this motor can provide a torque of 1.9 n-m at 800 rpm drawing a current of 2 a current are both zero at no load.) 1. with an armature supply voltage of 100 v, the motor is operated at 900 rpm. what is the motor torque? what is the mechanical power delivered by the motor? what is the current draw? what is the electrical power input? what is the energy efficiency of the motor? with an armature supply voltage of 100 v, the motor is operated at 1100 rpm (where it acts as a generator). what torque input is required? what mechanical power is required what current is generated? what is the electrical power generated? what is the energy efficiency of the motor acting as a generator? 2. with an armature supply voltage raised to 120 v, the motor is operated at 1000 rpm. what is the no-load speed? what is the motor torque? what is the mechanical power delivered by the motor? what is the current draw? what is the electrical power input what is the energy efficiency of the motor? 3.

What tightening torque should be used for a hexagonal head screw (not split-bolt) on a 250 kcmil conductor?