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Quick physics questions on power - just answering one would be so helpful!?
An elevator has a mass of 770 kg, not including passengers. The elevator is designed to ascend, at constant speed, a vertical distance of 20.0 m (five floors) in 15.0 s and it is driven by a motor that can provide up to 36 hp to the elevator. What is the maximum number of passengers that can ride in the elevator? Assume that an average passenger has a mass of 66.0 kg.
The total consumption of electrical energy in the United States is about 1.0 1019 joules per year.
(a) What is the average rate of electrical energy consumption?
W
(b) If the population of the United States is 260 million, what is the average rate of electrical energy per person?
W
(c) The sun transfers energy to the earth by radiation at a rate of approximately 1.0 kW per square meter to surface. If this energy could be collected and converted to electrical energy with 60% efficiency, how great an area would be required to collect the electrical energy used by the United States?
km^2
A baseball is thrown from the roof of a 30.0 m building with an initial velocity of magnitude 16.0 m/s and directed at an angle of 53.1° above the horizontal.
(a) What is the speed of the ball just before it strikes the ground? Use energy methods and ignore air resistance.
m/s
(b) What is the answer for part (a) if the initial velocity is at an angle 53.1° below the horizontal?
m/s
(c) If the effects of air resistance are included, will part (a) or (b) give a higher speed? Choose one:
No, the air resistance would have the same effect on the two balls and they would be slowed the same amount.
Pendulum. A small rock with mass 0.20 kg is fastened to a massless string with length 0.50 m to form a pendulum. The pendulum is swinging so as to make a maximum angle of 45° with the vertical. Air resistance is negligible.
(a) What is the speed of the rock when the string passes through the vertical position?
m/s
(b) What is the tension in the string when it makes an angle of 45° with the vertical?
N
(c) What is the tension in the string as it passes through the vertical?
N
A force of 500 N stretches a certain spring a distance of 0.240 m. What is the potential energy of the spring when a 65.0 kg mass hangs vertically from it?
J
A spring of negligible mass has force constant k = 1300 N/m.
(a) How far must the spring be compressed for 3.90 J of potential energy to be stored in it?
m
(b) You place the spring vertically with one end on the floor. You then drop a 1.70 kg book onto it from a height of 0.60 m above the top of the spring. Find the maximum distance the spring will be compressed.
m
A 2.00 kg piece of cheese is placed on a vertical spring of negligible mass and force constant k = 1600 N/m that is compressed 20.0 cm. When the spring is released, how high does the cheese rise from this initial position? (The cheese and the spring are not attached.)
m
You are asked to design a spring that will give a 1080 kg satellite a speed of 3.50 m/s relative to an orbiting space shuttle. Your spring is to give the satellite a maximum acceleration of 5.00g. The spring's mass, the recoil kinetic energy of the shuttle, and changes in gravitational potential energy will all be negligible.
(a) What must the force constant of the spring be?
N/m
(b) What distance must the spring be compressed?
m
A 0.75 kg book moves vertically upward a distance of 12 m, and then vertically downward 12 m, returning to its initial position.
(a) How much work is done by gravity during the upward motion of the book?
J
(b) How much work is done by gravity during the downward motion of the book?
J
(c) What is the total work done on the book by gravity during the complete round trip?
J
(d) On the basis of your answer to part (c), would you say that the gravitational force is conservative or nonconservative?
The gravitational force is non conservative.
The gravitational force is conservative.
Explain.
A 0.75 kg book slides on a horizontal table. The kinetic friction force on the book has magnitude 1.9 N.
(a) How much work is done on the book by friction during a displacement of 5.0 m to the left?
J
(b) The book now slides 5.0 m to the right, returning to its starting point. During this second 5.0 m displacement, how much work is done on the book by friction?
J
(c) What is the total work done on the book by friction during the complete round trip?
J
(d) On the basis of your answer to part (c),would you say that the friction force is conservative or nonconservative?
Friction is not a conservative force.
Friction is a conservative force.
A wooden rod of negligible mass and length 84.0 cm is pivoted about a horizontal axis through its center. A white rat with mass 0.800 kg clings to one end of the stick, and a mouse with mass 0.200 kg clings to the other end. The system is released from rest with the rod horizontal. If the animals can manage to hold on, what are their speeds
as the rod swings through a vertical position?
m/s
A 75.0 kg skier starts from rest at the top of a ski slope 85.0 m high.
(a) If frictional forces do -10.5 kJ of work on her as she descends, how fast is she going at the bottom of the slope?
m/s
(b) Now moving horizontally, the skier crosses a patch of soft snow, where µk = 0.2. If the patch is 85.0 m wide and the average force of air resistance on the skier is 160 N, how fast is she going after crossing the patch?
m/s
(c) The skier hits a snowdrift and penetrates 2.8 m into it before coming to a stop. What is the average force exerted on her by the snowdrift as it stops her?
N
Thank you so much!
6 Answers
- 1 decade agoFavorite Answer
Hey Jenna,
I was googling for the physics problem sets and I saw your question, haha
You are asked to design a spring that will give a 1080 kg satellite a speed of 3.50 m/s relative to an orbiting space shuttle. Your spring is to give the satellite a maximum acceleration of 5.00g. The spring's mass, the recoil kinetic energy of the shuttle, and changes in gravitational potential energy will all be negligible.
(a) What must the force constant of the spring be?
N/m
F=kx
5mg=kx
x=(5mg)/k
0.5mv^2 = 0.5kx^2
mv^2 = kx^2
mv^2 = k([5mg]/k)^2
mv^2 = k(25m^2g^2)/(k^2)
k = (25mg^2)/v^2
(b) What distance must the spring be compressed?
m
f=kx=ma
x=ma/k=5mg/k=50m/k
A 2.00 kg piece of cheese is placed on a vertical spring of negligible mass and force constant k = 1600 N/m that is compressed 20.0 cm. When the spring is released, how high does the cheese rise from this initial position? (The cheese and the spring are not attached.)
work=change in KE=total energy=PE at top (where KE=0)
0.5kx^2=mgh
h=(0.5kx^2)/(mg)
Source(s): http://www.physicsforums.com/archive/index.php/t-1... and my brain - Anonymous5 years ago
I suppose you mean the speed of sound is 343 m/s. t1 + t2 = t, time elapse before you hear the spash t1 = time for stone to hit the bottom of the well t2 = time for sound to reach you after the stone hits the bottom of the well. d1/v1 + d1/v2 = t 9.50m/v1 + 9.50 m/343 m/s = t 9.50 m/v1 + 9.50 m/343m/s = t eq. 1 v1 = Vavg, average velocity of stone v1 = Vavg = (Vi + Vf)/2 = (0 + Vf)/2 = 0 2gd1 = Vf^2 - Vi^2 Vf = sqrt[2gd1] Vf = sqrt[2(9.8)(9.50)] Vf = 13.6 m/s Therefore, v1 = (0 + 13.6)/2 = 6.8 m/s Going back to eq. 1: 9.50 m/6.8m/s + 9.50 m/343m/s = t eq. 1 t = 1.42 sec ANSWER Hope I help. teddy boy
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