Suppose, a ball of mass M is thrown upwards from a point A and it reaches up to the highest point B and returns back to point A, which one among the following is correct?
- A.Kinetic Energy at A = Potential Energy at B
- B.Kinetic Energy at A = Potential Energy at A
- C.Kinetic Energy at B = Potential Energy at B
- D.Kinetic Energy at B = Kinetic Energy at A
Correct answer
Explanation
The correct answer is A, Kinetic Energy at A = Potential Energy at B. Taking A as the reference level and ignoring air resistance, all the kinetic energy given at A turns into potential energy at the top, B.
Mechanical energy is conserved when only gravity does work. At A the ball has speed v and height zero, so its energy is all kinetic, ½Mv2. As it rises it slows down, and at the highest point B it stops for an instant, so its energy is all potential, Mgh. Equating the two gives ½Mv2 = Mgh, which also gives the height reached, h = v2/2g. On the way down the change runs in reverse.
B is wrong because at A the potential energy is zero while the kinetic energy is at its maximum.
C is wrong because at B the kinetic energy is zero while the potential energy is at its maximum.
D is wrong because the ball is at rest at B, so its kinetic energy there is zero, not equal to that at A.
Exam tip: at the top of a vertical throw, speed is zero, kinetic energy is zero and h = v2/2g.
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
Show answer
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.
Show answer
Liver cells turn the toxic ammonia released from the breakdown of amino acids into urea through the ornithine cycle, also called the urea cycle.
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
Show answer
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.
Show answer
It binds oxygen at its iron-containing haem groups and carries some carbon dioxide on its protein chains. Each haemoglobin molecule has four polypeptide chains and four haem groups, and each haem iron can hold one oxygen molecule, forming oxyhaemoglobin in the lungs.
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.
Show answer
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.
Read the full explanation →