Work Power and Energy Quiz
What is a spring dependent on? What does "k" represent" and what do we call it, what is it measured in?
- Force applied 2 spring - stifness of spring (k), which we call the spring constant (measured in N/m)
Convert 100 grams to kilograms
0.1 kg move 3 to left
Lorena's mass is 26 kg. She climbs the 4.8 m ladder of a slide and reaches a velocity of 3.2 m/s at the bottom of the slide. How much work was done by friction on Lorena? Assume that air resistance is negligible.
1089.92 J
Diego pulls a 4.5 kg sled across level snow with a force, F, of 215 N on a rope that is 35.0° above the horizontal, as shown in Figure 10-18. If the sled moves a distance of 64.9 m, how much work does Diego do?
11422.4 J
12. A monkey hangs from a spring attached to the ceiling of his cage. If he stretches the spring 40 cm when he hangs and the spring has a spring constant of 300 N/m, what is the monkey's mass?
12.2 kg
The third floor of a house is 9 m above street level. How much work is needed to move a 137 kg refrigerator to the third floor?
12083.4 J
A 200.0-Watt engine is used to pull a monkey sitting in a wagon forward across level ground. If there is no friction, and the mass of the monkey/wagon combo is 70.0 kg, how long will it take for the wagon to be traveling at 30.0 m/s?
158 s
A 11.5 kg test rocket is fired vertically from Cape Canaveral. Its fuel gives it a kinetic energy of 1970 J by the time the rocket engine burns all of the fuel. What additional height will the rocket rise? Assume that air resistance is negligible.
17.48 m
Convert 100 cm to m.
1m move 2 to left
A monkey driven car of mass 1500 kg is at the top of a tall parking structure 24 meters tall. Unfortunately, this car has no engine and must coast to the bottom of the ramp. If the velocity of the car is 12 m/s at the bottom, how much heat did the tires and brakes absorb during its descent? What is the efficiency of the descent? (What % of the initial energy was retained during the descent?)
2.45 x 10 ^5 J 30.6%
A car is driven at a constant speed of 80 km/h down a road. The car's engine delivers 45 kW of power. Calculate the average force that is resisting the motion of the car.
2025.020 N
A constant net force of 400 N is applied upward to a stone that weighs 35 N. The upward force is applied through a distance of 2.0 m, and the stone is then released. To what height, from the point of release, will the stone rise? Assume that air resistance is negligible.
22.86 m
A 500 kg monkey is standing on top of a muddy hill on a rainy day. The length of the slope is 100. m long and the height is 30.0 m. The monkey slips and begins to slide down the hill. What is the monkey's speed at the bottom of the hill? Assume friction is negligible.
24.2 m/s
Frank, a San Francisco hot dog vender, has fallen asleep on the job. A monkey comes by and starts his 300 kg cart rolling down the hill. If at point A, his cart has a velocity of 8.0 m/s and the cart has no friction, what would the velocity be at point B? HILL A H: 50 HILL B : 20
25.5 m/s
A monkey trapped in a metal cage has a mass of 50 kg. If this cage is being pulled down a 30-meter long ramp by a gorilla with a force of 1000 N, what was the height of the ramp? The force of friction is 200 N, and the velocity at the bottom of the ramp is 40 m/s.
32.7 m
Hakeem throws a 12.0 g ball straight down from a height of 2.0 m. The ball strikes the floor at a speed of 7.5 m/s. What was the initial speed of the ball? Assume that air resistance is negligible.
4.13 m/s
A spring with a spring constant 20 N/m is compressed 3 meters. If the energy from this compression is completely transferred to a 0.1 kg steel ball, what will be the resulting velocity of the ball? If a monkey launches it off the side of a 1.5 m table, with what speed will the ball hit the ground?
42.4 m/s 42.8 m/s
A lawn roller is pushed across a lawn by a force of 107 N along the direction of the handle, which is 22.5° above the horizontal. If 65.4 W of power is developed for 90.0 s, what distance is the roller pushed?
59.542 m
An engine moves a boat through the water at a constant speed of 12 m/s. The engine must exert a force of 5.0 kN to balance the force that the water exerts against the hull. What power does the engine develop?
60 kW
Haloke does 174 J of work lifting himself 0.294 m. What is Haloke's mass?
60.3 kg
A 14590 N car, m, is traveling at 25 m/s. The brakes are applied suddenly, and the car slides to a stop, as shown in Figure 11-17. The average braking force between the tires and the road is 7060 N. How far will the car slide once the brakes are applied? Assume that air resistance is negligible.
65.90 m
A cannon with a 200 cm long barrel applies a constant force of 120 N. If a monkey shoots the 2.7 kg cannonball straight up, what is the maximum height it reaches?
9.07m
Equations for Power
= KE / t = Work/t = F*v = ΔE/t
Which requires more work, carrying a 420 N backpack up a 200 m high hill or carrying a 210 N backpack up a 400 m high hill? A) Carrying the 210 N backpack requires more work. B) There is not enough information to decide. C) Carrying the 420 N backpack requires more work. D)Both require the same amount of work to carry. Why?
D)Both require the same amount of work to carry. When you use the equation W=Fd and input in 420 and multiply it by 200 you get 84,000J. When you input 210, the force, and multiply it by 400, the distance, you also get 84,000J.
Equation for work-energy theorom
Ei + Fd = Ef
cannon pointed straight up gunpowder pushes with 2000N for length of barrel (2.00) find the max height reached by the 10kg ball
Ei + W = Ef 0 + Fd = PEf Fd = mgh (2000)(2) = 10 (9.8) h= 40.8m
2000 kg car traveling at 40 m/s applies brakes. brakes apply force of 10,000N. What will the speed be after it has traveled 10m?
Ei + W = Ef KEi + Fd = KEf 1/2 (2000)(40)^2 + (-10,000)(10) = 1/2(2000)v^2 600,000 = 1000v^2 v= 24.5 m/s
mechanical energy and when is it equal?
Ei = Ef in the abscence of friction of other external forces
If 12 0.25kg apples are placed on a spring scale and it stretches 10cm what is the spring constant? How much energy is stored in the spring?
F= w of apples F=mg = kx mg = kx (on spring) 12 (0.25)(9.8) = k(0.1) divide 0.1 k = 294 N/m ------------------------------------------------------------- PEe = 1/2 kx^2 PEe = 1/2 (294) (0.1)^2 PEe = 147 (0.1)(0.1) 14.7(0.1) PEe = 1.47J
Hooke's Law
F=kx
In what units is work measured?
Joules
units for work
Joules
equation for kinetic energy
KE=1/2mv^2
3000 N piano dropped from 20m onto trampoline + compresses it 2.5 meters What is the spring constant of the trampoline?
KEe + PEi = KEf + PEf mghi = 1/2kxf^2 (3000)(20) = 1/2k(2.5)^2 60,000 = 3.125k k = 19,200 N/m
mechanical energy formula
KEi+PEi = KEf + PEf
1000g water ballon pulled back 60 cm sling with spring constant of 200N/m. what is the veocity of the water ballon when it leaves the slingshot?
KEi+PEi = KEf + PEf PEe = KEf 1/2 (200)(.60) = 1/2(1)v^2 36 = 0.5 v^2 divide by 0.5 v= 8.48 m/s
units for force
Newtons
How long would it take a 6W engine to lift a 12 kf box at constant speed to a heigh of 10m
P= W/t = Fd/t Force = weight of object 6 = 12(9.8)(10)/t t= 196s
equation for potential energy
PE=mgh
What is the force which does work? what does it represent?
PEe = 1/2kx^2 (energy stored in the spring)
Suzy Sailor is going down snowboarding down a steep slope. Suzi's mass is 60 kg and she starts at 5 m/s at the top, 220 m above the bottom of the hill. The ski run is 500 m long and there is a frictional force of 30 N b/w the snow and her board. How fast is she going when she reaches the bottom?
PEi+KEi +- W = KEf (60)(9.8)(220) + 1/2 (60)(5)^2 - (30)(500) = 1/2(60)v^2 129,360 + 750 - 15000 = 30vf^2 115,110 = 30v^2 divide by 30 3837 = vf^2 square root vf = 61.944 m/s or 62 m/s
Power
The rate at which work is done or energy is transferred
Which of the following baseballs (mass = 0.145 kg) has the largest amount of energy? a) a baseball traveling at 26.0 m/s b) a baseball dropped from a height of 33.0 meters c) a baseball launched from a slingshot with an elastic constant of 22 N/m that is stretched 2.0 meters.
a
Which spring requires a smaller force to stretch it 4.0 meters? (see Graph) a) Spring #1 b) spring #2 c) both the same
a
A 17.5 kg cart is moving with a velocity of 7.75 m/s down a level hallway. A constant force of -10.0 N acts on the cart, and its velocity becomes 3.20 m/s. Assume that air resistance is negligible. (a) What is the change in kinetic energy of the cart? (b) How much work was done on the cart? (c) How far did the cart move while the force acted?
a) -435.947 J b) -435.947 J c) 43.60 m
A 16 kg rock, m, is on the edge of a 115 m cliff, h, as shown in Figure 11-20. Assume that air resistance is negligible. (a) What potential energy does the rock possess relative to the base of the cliff? (b) The rock falls from the cliff. What is its kinetic energy just before it strikes the ground? (c) What speed does the rock have as it strikes the ground?
a) 18032 J b) 18032 J c) 47.48 m/s
An archer puts a 0.35 kg arrow to the bowstring. An average force of 203 N is exerted to draw the string back 1.3 m. Assume that air resistance is negligible. (a) Assuming that all the energy goes into the arrow, with what speed does the arrow leave the bow? (b) If the arrow is shot straight up, how high does it rise?
a) 38.83 m/s b) 76.92 m
Maricruz slides a 50 kg crate, m, up an inclined ramp 2.0 m long and attached to a platform 1.0 m above floor level, as shown in Figure 10-19. A 410 N force, F, parallel to the ramp, is needed to slide the crate up the ramp at a constant speed. (a) How much work does Maricruz do in sliding the crate up the ramp? (b) How much work would be done if Maricruz simply lifted the crate straight up from the floor to the platform?
a) 820 J b) 410 J
A force of 306.0 N is used to push a 145 kg mass 30.0 m horizontally in 3.00 s. (a) Calculate the work done on the mass. (b) Calculate the power developed.
a)9.180 kJ b) 3.06 kW
What does "x" in hookes law mean?
amt. of elongation/compression
4. Energy is the capacity for... a) producing power b) doing work c) being obnoxious d) none of these
b
5. How much work is done to stop a car, which has a kinetic energy of 5.0 x 105 J in 10 seconds? a) 5 x 104 J b) 5 x 105 J c) 5 x 105 W d) 5 x 104 W e) 2 x 10-5 J
b
What is the spring constant of spring #2? (see Graph) a) 80 N/m b) 200 N/m c) 50 N/m d) 100 N/m
b
What will be the kinetic energy of an arrow shot from a bow having a potential elastic energy of 40 Joules stored in it? a) less than 40 J b) 40 J c) more than 40 J
b
2. If the speed of an object is doubled, the kinetic energy of the object will... a) double b) triple c) quadruple d) increase by a factor of 8
c
An object at rest may have... a) speed b) velocity c) energy d) none of these
c
As a large pendulum swings back and forth, it reaches approximately the same height at the end of each swing. Why? a) Conservation of restoring force b) Conservation of momentum c) Conservation of energy d) Newton's 1st law
c
11. After reducing the following to its lowest form, what quantity is measured by this unit? (N*kg*m/s/s)(m)/ (J*kg) a) time b) velocity c) length d) acceleration e) force
d
6. If an object has kinetic energy, then it must also have ... a) an acceleration b) a force acting upon it c) height d) none of these
d
Convert km/h to m/s
divide by 3.6
kinetic energy
energy of motion
Work is
force x distance
What does potential energy depend on?
mass * gravity * height
What is kinetic energy dependent on?
mass and velocity
Potential Energy and Kinetic Energy are considered
mechanical energy
potential energy
stored energy
Energy
the ability to do work
What does Hooke's law state?
the force push/pull (on something stretchy) will equal the stiffness of spring will change shape
work-energy theorem
the work done on an object is = to the objects change in energy
Energy is
transferred when work is done
lbs ft/sec to HP to W
weight x height/ time then divide by 573 = Lbs ft Lbs ft (1HP/550Lbsft) = HP HP (746W/1HP) = W