# Shared Flashcard Set

## Details

Mechanics Final
N/A
63
Physics
05/04/2014

Term
 Could the work done on an object result in an increase of kinetic energy?
Definition
 Yes
Term
 Could you do no net work and yet get tired?
Definition
 Yes, for instance when lowering and lifting the same object many times
Term
 A conservative force in physics is
Definition
 a force that only depends on the initial and final points
Term
 The gravitational potential energy is (m is mass, h is height)
Definition
 mgh
Term
 Is friction a conservative force?
Definition
 no
Term
 The gravitational force between two masses applies
Definition
 for any masses in the universe
Term
 The drag forces and resistive forces are
Definition
 dependent on the speed
Term
 The terminal velocity is
Definition
 the constant speed at which an object moves in a fluid
Term
 Resistive forces on regular objects (rocks, raindrops, etc) in air are dominated by
Definition
 the pressure term
Term
 For objects moving in liquids you are normally in regime
Definition
 I
Term
 The direction of the force respect to the increase of potential energy is
Definition
 opposite
Term
 If we knew the potential energy could we get the force?
Definition
 yes
Term
 From the energy equation in a spring mass system we can derive
Definition
 the equation for simple harmonic motion
Term
 An object moves near the bottom of a frictionless spherical bowl. If the object starts from rest and you let it go the motion would be
Definition
 simple harmonic motion
Term
 In an oscillating pendulum is the tension doing any work?
Definition
 no
Term
 Why did the smaller circular track fail the prediction for small oscillations, while the large air track did not?
Definition
 the ball roll in the small track while the mass did not roll in the large one
Term
 The velocity to escape the gravitational pull of the Earth and never fall back is
Definition
 11.2 km/s
Term
 If the total energy available to an object that wants to leave the Earth is less than zero we call the possible orbit
Definition
 bound
Term
 The period of rotation of the space shuttle orbit around the Earth was
Definition
 90 minutes
Term
 A person is riding a bicycle. The power required to maintain certain speed is force times velocity. The force due to air friction is the air drag and it is proportional to the velocity squared. The power needed to double the speed is
Definition
 8 times
Term
 How many watts per square meter does the Sun provide to the Earth?
Definition
 1400 watts
Term
 If a particle changes its momentum
Definition
 a force must have acted on it
Term
 The change of total momentum of a system of particles is equal to
Definition
 the sum of external forces only
Term
 If the net force on a system of particles is zero, we say that the net momentum is
Definition
 constant
Term
 In collision of particles with no outside forces we say that
Definition
 the kinetic energy is not always conserved
Term
 The center of mass is at point
Definition
 that behaves as if all the mass of the object was concentrated there
Term
 Two ball with same mass collide with each other in an elastic collision. One ball was at rest before collision, what happens after collision?
Definition
 the ball at rest moves while the incoming ball stops
Term
 A collision of particles as seen from the center of mass has momentum zero
Definition
 before and after collision
Term
 As seen from the center of mass, in an elastic collision, the speeds of particles after collision are:
Definition
 the same as before but with opposite signs
Term
 The ballistic pendulum is used to measure
Definition
 the speed of a bullet
Term
 What is impulse?
Definition
 a change in momentum
Term
 The engines in rocket Saturn spit out gas at the speed of
Definition
 2.5 km/s
Term
 Two identical rockets with burn the same amount of fuel and increase their speed by the same amount; one started from rest and one was already moving. Which rocket increases its kinetic energy more?
Definition
 the rocket that had an initial speed
Term
 n circular motion, the tangential acceleration results in a change of
Definition
 speed of the particle
Term
 The moment of inertia for a set of masses is the sum of
Definition
 each mass times the distance square of this mass to the axis of rotation
Term
 Can energy be stored in a rotating object?
Definition
 Always
Term
 The Crab pulsar rotational speed is
Definition
 slowing down
Term
 The angular momentum of a point-like object depends on
Definition
 the location of the origin of observer
Term
 What makes the angular momentum of a point-like object change as seen by the same observer?
Definition
 a torgue
Term
 If an object spins around its center of mass then its the angular momentum is
Definition
 the same for all observers located anywhere
Term
 If an object is free of external torques and is spinning, what would happen if the object increases, by any means, its moment of inertia?
Definition
 it will slow down
Term
 A star collapses after it runs out of nuclear fuel. What could happen to it?
Definition
 it could be come a white dwarf, neutron star or a black hole
Term
 The angular momentum of a point-like object changes if there is
Definition
 an external torque
Term
 The angular momentum of a meter stick about the center of mass is
Definition
 the same for all centers of rotation
Term
 A ruler is hit at a point away from its center of mass. After the hit the center of mass will move
Definition
 in a straight line
Term
 A hula hoop is made to oscillate about a point at its edge. The period of oscillation does not depend on
Definition
 the mass
Term
 The general orbit of a planet around the Sun is
Definition
 elliptical
Term
 Kepler found that planets move so that
Definition
 they trace equal areas in equal times
Term
 If for an orbit of a satellite or planet the total energy is negative we have
Definition
 an ellipse
Term
 If a sandwich is in a circular orbit and we want to change it to another orbit by slowing it down in a direction tangent to the circle the period of the sandwich will
Definition
 decrease
Term
 f an object that emits light approaches you its as seen by you light is
Definition
 blue shifted
Term
 What fraction of the stars are binary?
Definition
 1/2
Term
 Inside the event horizon of a black hole
Definition
 an object is trapped forever
Term
 When an object is in pure roll the speed of the center of mass is
Definition
 equal to the angular speed times radius
Term
 Two solid cylinders of the same mass, but one is smaller than the other, roll down an inclined plane, which one gets to the bottom first?
Definition
 they arrive at the same time
Term
 The angular momentum when changing moves in the direction
Definition
 of the torque
Term
 A bicycle wheel is spinning about its axis. If we support the wheel with a string at the end of one handle, what would happen?
Definition
 the wheel will precess (rotate) about the axis of the string
Term
 The spin angular momentum has the property of
Definition
 stabilizing things
Term
 What are the conditions for equilibrium of a rigid body?
Definition
 sum of forces and sum of torques both equal zero
Term
 A ladder is set on the floor near a wall. The ladder is at a critical angle so that it is ready to slide. A person steps at the bottom of the ladder then the ladder becomes
Definition
 more stable
Term
 If you have a tube with and a rope wrapped around it so that the ends of the rope support a load each. Due to the friction the rope experiences with the tube we could
Definition
 put a very large load on one end of the rope and small load on the other
Term
 If you have an object with random shape. How could we find its center of mass?
Definition
 Find the point where two vertical equilibrium lines meet
Term
 A ropewalker to be very stable could use a long bent bar with extra weight at the ends so that
Definition
 the center of mass is below the rope
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