fundamentals 6 Flashcards
Sketch a free body diagram for a car that is moving to the right and skidding to a stop.
You should have drawn an upward arrow for the force of the road on the car (i.e. the normal force); you should have drawn a downward arrow for the force of the earth on the car (the weight); and you should have drawn a leftward arrow for the force of the road on the car (i.e. the friction force). There should be no arrow to the right - motion is not a force.
What are the units of rotational kinetic energy?
joules. (ALL forms of energy have units of joules.)
An object experiences only two forces: 20 N to the east, and 20 N to the north. What is the magnitude of the net force on the object?
28 N, or 20-root-2 N. (Force is a vector quantity, so perpendicular forces add using pythagoras.)
A system consists of two objects, and experiences no net external force. Describe the motion of the system’s center of mass.
the center of mass moves at constant velocity. (No net external force means the system has no acceleration by F = ma, and no acceleration means no change in velocity for the system’s center of mass.)
What is found by the area under a force vs. displacement graph?
work.
Planet X has a gravitational field that is 1/8 that on earth. Joel has mass 100 kg on earth. What is his mass on Planet X?
100 kg. (Mass is the amount of material contained in an object, which doesn’t change based on gravitational field.)
Two carts collide and bounce off one another. (a) Was momentum conserved in the collision? (b) Was mechanical energy conserved in the collision?
yes; we don’t know. (Momentum is always conserved in a collision. Mechanical energy would be conserved if the collision is elastic. We don’t know whether or not the collision is elastic! Yes, in an elastic collision objects must not stick together, but not all collisions where objects bounce off one another are elastic. Either we have to be told explicitly that a collision is elastic, or we have to do a calculation comparing mechanical energy before and after collision to show the collision to be elastic.)
Two carts collide and stick together. (a) Was momentum conserved in the collision? (b) Was mechanical energy conserved in the collision?
yes; no. (Momentum is always conserved in a collision; mechanical energy is only conserved in an elastic collision, and when objects stick together, the collision may never be elastic.)
Write the equation for the potential energy stored in a spring
(1/2)kx^2.
Define the period of simple harmonic motion.
the time for the object to complete one cycle of harmonic motion
