EN Energy 2 Test BB
What amount of work is done on a chair that is pushed across the floor by a horizontal 30-N net force?
2670 J
About how efficient is a typical gasoline burning engine?
30%
How much work is done on a 60N box of books that you carry horizontally across a 6 meter room?
360J
How much work is done on a 20N crate that you lift 2 meters?
40 J
How much power is expended if you lift a 60 N crate 10 meters in 1 second?
600 W
An arrow is a bow has 70 J of potential energy. Assuming no loss of energy to heat, how much kinetic energy will it have after it has been shot?
70 J
How many joules of work are done on a box when a force of 25 N pushes it 3m?
75 J
Which has greater kinetic energy, a car traveling at 30km/h or a half mass car traveling at 60km/h?
The 60 km/h car
The energy an object has by virtue of its motion is its kinetic energy.
True
The rate at which work is done is called the power.
True
The unit for work is called the joule
True
The unit of power is the watt.
True
Using an inclined plane is an effective way to lift a heavy object that you otherwise couldn't lift.
True
If you lift one load up two stories, how much work do you do compared to lifting one load up only one story?
Twice as much
If you lift two loads up one story, how much work do you do compared to lifting just one load up two stories?
Twice as much
The unit of power is called the
Watt
Power is defined by
Work done in an object divided by the time taken to do the work
A pendulum swings back and forth
a. at the end points of its swing, its energy is all potential. b. at the lowest part of its swing, its energy is all kinetic. c. kinetic energy is transformed into potential energy. d. potential energy is transformed into kinetic energy.
A heavy object and a light object are released from rest at the same height and time in a vacuum. As they fall, they have equal
none of the below a. energies. b. weights. c. momenta.
Kinetic energy of an object is equal to
one half the product of its mass times its speed squared 1/2mv^2
A job is done slowly, and an identical job is done quickly. Both jobs require the same amount of work but different amounts of
power
it takes 80 J to push a large box 8 meters across the floor. assuming the push is in the same direction as the move, what is the magnitude of the force on the box?
10 N
A 60 N object moves at 1 m/s. Its kinetic energy
30 J
What is the work done in lifting 75 kg of blacks to a height of 10 meters
750 J
How much power is required to do 40J of work on an object in 5 seconds?
8 W
Rockets are launched from an airplane in the forward direction of motion. The kinetic energy of the plane will be
Decreased
A popular toy consists of an aligned row of identical elastic balls suspended by strings so they touch each other. When two balls on one end are elevated and released, they slam into the array of balls and two balls pop out the other side. If instead, one ball popped out with twice the speed, this would be a violation of the conservation of
Energy
An object at rest may have
Energy
A pulley system can change only direction, it can't multiply forces as well.
False
In physics, the amount of work done on an object is the product is the force exerted on the object times the times the time object moves
False
The energy an object has by virtue of its location is its potential energy.
False
The rate at which work is done is called energy
False
In physics, work id defined as
Force times distance
How much farther will a car traveling at 100 km/s skid than the same car traveling 50 km/s
Four times as far
If Nellie Newton pushes an object with twice as much force for twice as much the distance, she does
Four times the work
The unit of work is the
Joule
A ball is thrown into the air with 100 J of kinetic energy, which is transformed to gravitational potential energy at the top of its trajectory. When it returns to its original level after encountering air resistance, its kinetic energy is
Less than 100 J
Potential energy is the energy an object has because of its
Location
The ratio of output force to input force of a simple machine is called the
Mechanical advantage
The ratio of useful work output to total work input is called the
Mechanical advantage
An object that has kinetic energy must be
Moving
The amount of potential energy possessed by an object is equal to
The work done in lifting it
Energy transformations from one form to another with no loss or gain.
True
A woman can lift barrels a vertical distance of 1 meter or can roll them up a 2- meter long ramp to the same elevation. if she uses the ramp, the applied force is
half as much
When a cars speed triples, its kinetic energy is
increased by nine times
A machine puts out 100 watts of power for every 1000 watts put into it. The efficiency of the machine is
10%
suppose a moving car has 3000J of kinetic energy. If the car's speed doubles, how much kinetic energy will it then have?
12,000 J
A person on a roof throws one ball downward and an identical ball upward at the same speed. The ball thrown downward hits the ground with 140 J of kinetic energy. How much kinetic energy does the second ball hit the ground with?
140 J
Energy is changed from one to another with no net loss or gain
Always true
Which requires more work: lifting a 70kg sack vertically 2 meters or lifting a 35kg sack vertically 4 meters?
Both require the same amount of work
An object that has kinetic energy must have
momentum
a pulley system can
multiply the force
A small economy car (low mass) and a limousine (high mass) are pushed from rest across a parking lot, equal distances with equal forces. The car that receives more kinetic energy is the
neither one - they receive the same amount of kinetic energy.
