Energy Conservation
Work
Springs
Conceptual
Power
100
A rock is thrown straight up. Neglecting air resistance, what happens to the total mechanical energy of the rock as it rises?
It remain constant.
100
Which SI unit is defined as a Newton-meter, which is the unit of work?
Joule (J)
100
A guardrail spring with a spring constant k = 100N/m is compressed by 0.5m. How much energy is stored in the spring?
12.5 J
100
A 10 pound and 5 pound bowling balls are rolled up a 1.5 meter tall ramp at the same initial speed. Which will have more potential energy when both balls are at the top of the ramp?
The 10 pound ball.
100
What is the SI unit of power?
Watt
200
An engineer designs a playground slide such that the speed a child reaches at the bottom does not exceed 6.0 m/s. Determine the maximum height (h) the slide can be.
1.8 m
200
Jason pushes an object with force F over distance D. Peter pushes the same object with twice the force (2F) for twice the distance (2D). Peter does how many times the work of Jason?
4 times the work
200
A 6kg mass hangs at rest, causing a vertical spring to stretch by 20cm. Calculate the spring constant, k.
294 N/m
200
Two balls, one with twice the mass of the other, are dropped from the same height. When they hit the ground, how does the kinetic energy of the lighter ball compare to the heavier ball?
The lighter one has one-half as much kinetic energy as the other.
200
How much power is expended if you lift a 50N rock 10 meters in 1 second?
500W
300
How much energy is dissipated (converted into non-mechanical forms) in braking a 1000kg car to a stop from an initial speed of 20m/s?
2000,000J
300
Mike pushes a lawn mower 0.5m with a 200N force directed at 30 degrees below the horizontal. Calculate the work done by Mike.
86.6 J
300
A spring hangs from a ceiling. A mass of 2kg is attached to the spring and it stretches 0.22 m. If a 5kg mass is attached to the same spring instead of the 2kg one, what is the new stretch length?
0.55 m
300
For a box pulled across a rough floor at constant velocity, what is the net work done on the object?
Zero
300
A 51kg woman runs up a flight of stairs, achieving a net upward displacement of 5.0m in 5.0s. Approximately what average power did she exert?
500W
400
A 5.0kg object is launched vertically upward from the ground with an initial velocity of 15.0 m/s. The upward motion is resisted by an average air friction force of 5.0N. Using the Law of Conservation of Energy, calculate the maximum height the object reaches.
10.4 m
400
A 10kg box is pulled up a 30 degree incline of length 5.0m by a constant force of 100N parallel to the incline. If a kinetic friction force of 20N opposes the motion, what is the net work done on the box?
155 J
400
A block of mass m=2.0kg is compressed against a horizontal spring k=500 N/m by a distance x=0.40m. When released, the block slides frictionlessly across the floor and then launches horizontally off a table of height H=1.25m. What is the horizontal distance (R) (range) the block travels from the edge of the table before hitting the ground?
2.0m
400
A small block of mass (m) starts from rest at the top of a frictionless ramp of height (h). It slides down the ramp and enters a vertical circular loop of radius$R. Assuming the block moves just fast enough to make it around the loop without falling off at the highest point, derive the necessary height (h) from which the block must be released in terms of the radius (R).
2.5R
400
A concrete block is pulled 10.0m across a frictionless surface by a rope with 10N of tension. If the net work done is 86.6J, and the time taken is 5.0s, calculate the power generated by the horizontal component of the tension force.
17.32W
500
A string is tied to a 2kg mass and suspended from a ceiling to form a pendulum (as shown in the picture). If the pendulum is pulled 30 degrees from the vertical and released, how fast is it moving at the bottom of it's path?
1.64 m/s
500
A 10.0kg crate is pulled a distance of 5.0m across a rough horizontal floor by a constant rope tension of 75N applied at an angle of 37 degrees above the horizontal. The crate starts from rest. If the coefficient of kinetic friction between the crate and the floor is 0.40, what is the final speed of the crate?
6.2 m/s
500
A 1 kg block rests against a 100 N/m spring. The spring is compressed 0.25m and the block is released. The block then moves up an 15 degree inclined plane. If the surface of the inclined plane has a kinetic coefficient of friction of 0.1, how high up the ramp does the block go?
0.232m
500
A block is pushed across a rough horizontal surface by a force F over a distance (d). In which of the following three scenarios is the final kinetic energy (K) of the block the greatest?
Scenario 1: The force F is applied horizontally.
Scenario 2: The force F is applied at an angle above the horizontal.
Scenario 3: The force F is applied at an angle below the horizontal.
Scenario 2
500
A machine lifts a 500kg piano to a vertical height of 10m in 8.0s. The machine operates at an overall efficiency of 70%. What is the minimum power input required for the machine to complete this task?
8750 W