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Physics Problems

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Need help with these physics questions. Please provide explanations with answers.

1. On February 20, 1962, John Glenn became the first American to orbit Earth. If John Glenn weighed 640 N on Earth's surface, a) how much would he have weighed if his Mercury spacecraft had (hypothetically) remained at twice the distance from the center of Earth? b) Why is it said that an astronaut is never truly "weightless?"

2. Mr. Gewanter, whose mass is 60.0 kg, is doing a physics demonstration in the front of the classroom. a) How much gravitational force does he exert on 55.0-kg Martha in the front row, 1.50 m away? b) How does this compare to what he exerts on 65.0-kg Lester, 4.00 m away in the back row?

3. Astrologers claim that your personality traits are determined by the positions of the planets in relation to you at birth. Scientists argue that these gravitational effects are so small that they are totally insignificant. Compare the gravitational attraction between you and Mars to the gravitational attration between you and your 70.0-kg doctor at the moment of you birth, if the doctor stands 0.500 m away. NOTE:MM = 6.42 x 1023 kg, dE-M = 7.83 x 1010 m. This is the average distance between Earth and Mars. This distance varies as the two planets orbit the sun.

4. Our galaxy, the Milky Way, contains approximately 4.0 x 1011 stars with an average mass of 2.0 x 1030 kg each. How far away is the Milky Way from our nearest neighbor, the Andromeda Galaxy, if Andromeda contains roughly the same number of stars and attracts the Milky Way with a gravitational force of 2.4 x 1030 N?

5. Tides are created by the gravitational attraction of the sun and moon on Earth. Calculate the net force pulling on Earth during a) A new moon, b) a full moon, c) a first quarter moon. The diagram is intended to help your understanding of the situation but is not drawn to scale. (mM = 7.35x 1022 kg, mE= 5.98x 1024 kg, mS = 1.99 x 1030 kg, dE-M = 3.84 x 108 m, dE-S = 1.50 x 1011 m)

6. Two cars, one twice as heavy as the other, move down a hill at the same speed. Compared to the lighter car, the momentum of the heavier car is ________________.

7. On April 15, 1912, the luxury cruise liner Titanic sank after running into an iceberg. What was the cruise liner's speed when it collided with the ice berg if it had a mass of 4.23 x 108 kg ship and a momentum of 4.9 x 109 kg m/s?

8. Suppose you are traveling in a bus at highway speed on a nice summer day and the momentum of an unlucky bug is suddenly changed as it splatters onto the front window.
a) Compared to the force that acts on the bug, how much force acts on the bus. (more) (the same) (less)
b) Although the momentum of the bus is very large compared to the momentum of the bug, the change in momentum of the bus compared to the change in momentum of the bug is (more) (the same) (less)
c) Which experiences the greater acceleration ( HINT: Think of Newton's 2nd Law)? (bus) (both the same) (bug)
d) Which, therefore, suffers the greater damage? (bus) (both the same) (the bug of course!)

9. A 4.5-kg ham is thrown into a stationary 15-kg shopping cart. At what speed will the cart travel if the ham had an initial speed of 2.2 m/s?

10. Make two event chains showing what happens when a rolling ball (Ball 1) hits a resting ball (Ball 2) Use the phrases: gains momentum, hits Ball 2, is hits by Ball 1, loses momentum, rests, rolls, slows, down, stars rolling.

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Solving Physics Questions

1. Give an example of a situation in which there is a force and a non-zero displacement, but the force does no work. Explain why it does no work.
2. What is a conservative force?
3. (a) Calculate the work done on a 1500 kg elevator by its cable to lift it 40.0 m at constant speed, assuming friction averages 100 N. (b) What is the work done on the elevator by gravity in this process? (c) What is the total work done on the elevator?
4. A shopper pushes a grocery cart 20.0 m at constant speed on level ground, against a 35.0 N frictional force. He pushes in a direction 25.0 degrees below the horizontal. (A) What is the work done on the cart by friction? (B) What is the work done on the cart by gravity? (C) What is the work done on the cart by the shopper? (Remember the Work-Kinetic Energy Theorem.) (D) Find the force the shopper exerts, giving both the x- and y-components, and the magnitude of the force. (E) What is the total work done on the cart?
5. Compare the kinetic energy of a 20,000 kg truck moving at 110 km/h with that of an 80.0 kg astronaut in orbit moving at 27,500 km/h.
6. (a) Calculate the force needed to bring a 950 kg car to rest from a speed of 90.0 km/h in a distance of 120 m. Use the work-kinetic energy theorem (b) Suppose instead the car hits a concrete abutment at full speed and is brought to a stop in 2.00 m. Calculate the force exerted on the car and compare it with the force found in part (a).
7. Suppose a bicycle rolls down a hill, starting from rest. It drops an altitude of 4.0 m, ending up on level ground. The mass of the bicyclist plus bike is 70.0 kg. Assume that friction can be ignored. (A) Find the potential energy lost by the bicycle and rider. (B) Find the speed of the bicycle when it reaches level ground. (C) Repeat (B), assuming that this time the bicycle starts with an initial speed of 4.0 m/s. (D) Suppose frictional forces dissipate 400 J of energy while the bike rolls down the hill. Find the speed of the bicycle when it reaches level ground in this case. (Again, assume an initial speed of 4.0 m/s.)
8. A 60.0-kg skier with an initial speed of 12.0 m/s coasts up a 2.5-m-high hill as shown. (A) Find his final speed at the top, assuming no friction is involved. (Use energy methods, not the equations for constant acceleration.) (B) Now suppose the coefficient of friction between skier and snow is 0.08. Again find his speed at the top of the hill. (Don't worry about energy lost on the flat at either end --- just find the energy dissipated by friction on the 35-degree slope and use this in your calculations.)

9. A cart is rolling without friction on a platform, hooked to a hanging mass with a string which runs over a pulley, as shown in the diagram. The mass m_c of the cart is 0.35 kg, and the hanging mass is 0.050 kg. (A) How much work does the force of gravity do on the system when the hanging mass moves from a height of 0.80 m to a height of 0.30 m? (B) Assuming it starts from rest, find the speed of the cart after 0.50 m of travel. Use the information from part (A), and energy considerations. Do not use Newton's laws.

10. Suppose we have a spring whose force as a function of compression is shown in the graph. We place a ball of mass 0.600 kg on top of the spring and compress it by 0.25 m from its relaxed length. We then let the ball go. When the ball is released, its height above the floor is 0.10 m.

(A) Find the spring constant of the spring.
(B) Determine the potential energy of the spring when compressed.
(C) Find the highest point the ball reaches in its flight.
(D) Determine the velocity of the ball just as it leaves the spring: that is, just as the spring is fully relaxed.

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