An astronaut whose weight on the Earth is 600 N experiences weightlessness on International Space Station orbiting around the Earth. It means that
- A.acceleration of the astronaut is zero
- B.normal reaction of the space-station floor on the astronaut is zero
- C.gravitational pull of earth on the astronaut is zero
- D.space station applies a centrifugal force on the astronaut
Correct answer
Explanation
The correct answer is B, the normal reaction of the floor on the astronaut is zero. The weight we feel is really the push of the floor on us, and in orbit that push disappears.
The space station and the astronaut are both in free fall around the Earth. Gravity pulls them down at the same rate, so the floor never presses against the astronaut's feet and a weighing scale would read zero. At the station's height of about 400 km, gravity is still roughly 90 percent of its value at the surface; it is busy bending their path into a circle.
A is wrong because the astronaut is accelerating all the time, towards the Earth's centre, which keeps the orbit curved.
C is wrong because the Earth's pull is still strong there; without it the station would fly off in a straight line.
D is wrong because centrifugal force is only an apparent force in a rotating frame; the station applies no such force.
Exam tip: weightlessness means free fall, zero normal reaction, not zero gravity.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Read the full explanation →Which one of the following statements is correct?
- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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