Chapter 14- take home test
3730 watts equals about how many horsepower?
5
The ideal mechanical advantage of a wheel and axle is found by
dividing the radius of the wheel by the radius of the axle
A machine is a device that can multiply
force
If you do work on an object in half the time, your power output is
twice
If you have to apply 40 N of force on a crowbar to lift a rock that weighs 400 N, what is the actual mechanical advantage of the crowbar?
10
It takes 40 J to push a large crate 4 m across a floor. The force exerted on the crate is
10 N
A hydraulic jack is used to lift an automobile. If the input force is 200 N over a distance of 1 meter, the output force over a distance of 0.1 meter is ideally
1000 N
If you exert 100 J to lift a box in 50 s your power output is
2 W
A pulley has two supporting strands. To lift a load 1 meter means you will have to pull a distance
2 m
A 120-m long ski lift carries skiers from a station at the foot of a slope to a second station 40 m above. What is the IMA of the lift?
3
If you exert 6 N across a distance of 2 m in 3 s you'll deliver a power of
4 W
A music console is pushed 2 m by a force of 20 N. The work done on the console is
40 J
An example of a compound machine is a
Bicycle
Which requires more work: lifting a 50-kg sack vertically 2 m or lifting a 25-kg sack vertically 4 m?
Both require the same amount of work
A pulley system can
Change the direction of a force and multiply a force
The power expended for a barbell raised 2.0 m in 2 s is
Not enough information
Work is done by gravity on a bowling ball that rolls
On a sloped surface
The efficiency of a machine is always less than 100% because
Some work input is lost to friction
A machine can make work easier for you
by changing the direction of your force
A common pulley acts similar to a
common lever
Reducing friction in a machine
increases its efficiency
An inclined plane reduces the effort force by
increasing the distance through which the force is applied
The actual mechanical advantage of a machine
is less than the ideal mechanical advantage of the machine
A machine is classified as a compound machine if it
is made up of two or more simple machines that operate together
Power is defined as the
work done divided by the time to do the work
A 750-W motor might also be rated as a
1-horsepower motor.
A machine puts out 100 W of power for every 1000 W put into it. The efficiency of the machine is
10%
A motor with an efficiency of 75% must supply 240 J of useful work. What amount of work must be supplied to the motor?
320 J
Using 1000 J of work, a toy elevator is raised from the ground floor to the second floor in 20 s. How much power does the elevator use?
50 W
A mechanical device requires 420 J of work to do 230 J of work in lifting a crate. What is the efficiency of the device?
55%
If you exert a force of 700 N to walk 6 m up a flight of stairs in 6 s, how much power do you use?
700 W
A clerk can lift containers a vertical distance of 1 m, or roll them up a 2-m long ramp to the same elevation. With the ramp, the applied force needed is
Half as much
If you know the input distance and output distance of a machine, you can calculate the
Ideal mechanical advantage
You do work on a cart loaded with groceries. If you do this work in one-third the usual time, you expend
Three times the usual power
A 1000-kg car and a 2000-kg car are hoisted the same vertical distance in a service station. Raising the more massive car requires
Twice as much work
If you push an object twice as far while applying the same force, you do
Twice as much work
When you push an object a certain distance while applying twice the force, you do
Twice as much work
An axe is a example of a(n)
Wedge
An automobile steering wheel is an example of a(n)
Wheel and axle
Lifting a 100-N load with 50 N of force lifts it
half as high
When a machine does work, it cannot
increase a force and increase the distance a force moves an object
The power of a machine measures
its rate of doing work
The ideal mechanical advantage of a pulley system is equal to the
number of rope segments supporting the load
If you push for an hour against a stationary wall, you do no work
on the wall