The NDA (National Defence Academy) exam is a prestigious military entrance test in India.
A thin disc and a thin ring, both have mass M and radius R. Both rotate about axes through their center of mass and are perpendicular to their surfaces at the same angular velocity. Which of the following is true ?
a. The ring has higher kinetic energy
b. The disc has higher kinetic energy
c. The ring and the disc have the same kinetic energy
d. Kinetic energies of both the bodies are zero since they are not in linear motion
Let there be an object having some chemicals in it. It starts moving with a uniform velocity v and a chemical reaction starts happening. In this case, which of the following statement/s is/are correct ? 1. Chemical reactions happening in the system cannot change the velocity v of the center of mass of the object. 2. Chemical reactions happening in the system cannot change kinetic energy of the particles inside with respect to the center of mass of object. Select the correct answer using the code given below—
a. 1 only
b. 2 only
c. Both 1 and 2
d. Neither 1 nor 2
a. Thermal conduction
b. Thermal convection
c. Thermal radiation
d. Both, thermal conduction and radiation
Which one of the following statements regarding Ohm’s law is not correct ?
a. Ohm’s law is an assumption that current through a conductor is always directly proportional to the potential difference applied to it.
b. A conducting device obeys Ohm’s law when the resistance of a device is independent of magnitude and polarity of applied potential difference.
c. A conducting material obeys Ohm’s law when the resistance of material is independent of the magnitude and direction of applied electric field.
d. All homogeneous materials obey Ohm’s law irrespective of whether the field is within range or strong.
When a ball bounces off the ground, which of the following changes suddenly ? (Assume no loss of energy to the floor)
a. Its speed
b. Its momentum
c. Its kinetic energy
d. Its potential energy
Which one of the following compounds does not exhibit a different oxidation number of the same element ?
a. Glass is often said to be a supercooled liquid
b. Glass has no definite melting point
c. Soda glass is harder than pyrex glass
d. Boron is present in pyrex glass
a. Both boiling and evaporation are surface phenomena
b. Boiling is a surface phenomenon, but evaporation is a bulk phenomenon
c. Both boiling and evaporation are bulk phenomena
d. Boiling is a bulk phenomenon, but evaporation is a surface phenomenon