Physics Test 2
Two identical balls are rolled across tracks A and B. The depth of the dip in track B and the height of the bump in track A are the same. Both balls are initially moving at the same speed: what is their final speed and who finishes first?
Their final speeds are the same, but ball B finishes first.
Three cars (F,G,H) are moving with the same velocity, and slam on the brakes. The most massive car is F and least massive is H. Assuming all three have identical tires, for which car travels the longest distance to skid to a stop?
They all travel the same distance
The total mechanical energy of a circular orbit
is never posative
Two particles interact by conservative forces. In addition, an external force acts on each particle. They complete round trips, ending at the points where they started. Which of the following must always have the same values at the beginning and end of this trip?
The potential energy of the two- particle system
Why can't we write potential functions for non-conservative forces?
Because the work done by non-conservative forces depend on the path.
The blocks (P,Q,R) are initially at rest. Block P is the most massive and block R is the least massive. Identical horizontal forces push each block for five meters causing them to accelerate. Assuming the coefficient of friction between the blocks and ground is the same for all three blocks, which block will have the highest amount of kinetic energy?
Block R
E=
E initial plus Delta E
m2=4m1. If the distance between them is doubled, the gravitational force between them is -
1/4 as big
T or F: Mechanical energy is always posative?
False
T or F: If the work done by a force is zero than we know that the force MUST be 0
False for all forces
Yes or No: If you pick up a suitcase and put it down have you done any work?
No, because the path is perpendicular to the work.
Two objects, one of mass m and the other of mass 2m, are dropped from the top of a building. When they hit the ground:
The heavier one will have twice the kinetic energy of the lighter one.
T or F: The only way for the dot product of two vectors to be negative is for the angle between them to be greater than 90 degrees.
True
In order to do work on an object
the object must move
A force of 10N holds an ideal spring with a 20N/m spring constant in compression. The potential energy stored in the spring is:
2.5J
Three balls are fired with equal masses are fired at equal speeds at different angles (45 d, 60 d, and straight up). They all have sufficient speed to reach the dotted line. Rank in order from the largest to the smallest their speed as they cross the dashed horizontal line.
All velocities are the same.
Three cars (F,G,H) are moving with the same velocity, and slam on the brakes. The most massive car is F and least massive is H. Assuming all three have identical tires, for which car does friction do the most work?
Car F
T or F: If the dot product between two vectors is 1 then the vectors must be perpendicular
False
When we speak of a conservative force, what is being conserved?
Mechanical energy ( Kinetic and potential - the path is dependent)
Yes or no: Must you do work to whirl a ball around on the end of a string?
No, because the path is perpendicular to Force.
Two cyclists, who weigh the same and have identical bicycles, ride up the mountain. Joe rides straight up the mountain and Bob takes a longer rout that is not as steep and it takes Bob longer to get to the top. Ignoring friction and wind resistance, what is the amount of work done?
The amount of work done by Joe is equal to the amount done by Bob, but the average power exerted by Joe is greater than that of Bob.
