Physics - Study Mode

[#561] A body of 4.0 kg is lying at rest. Under the action of a constant force, it gains a speed of 5 m/s. The work done by the force will be ________
Correct Answer

(A) 50 J

Explanation

Solution: Work done = 1/2*m*V 2 =1/2*4*5 2 = 1/2*4*25 = 2*25 = 50 J

[#562] If the velocity of a body is halved its kinetic energy ________
Correct Answer

(B) Becomes 1/4 th

Explanation

Solution: When velocity is halved, its kinetic energy becomes 1/4th.

[#563] Solar energy is converted into chemical energy during
Correct Answer

(B) Photosynthesis

Explanation

Solution: Solar energy is converted into chemical energy during photosynthesis.

[#564] In which of the following cases, kinetic energy is being used in performing work ?
Correct Answer

(B) Driving a car to cover a distance

Explanation

Solution: In driving a car to cover a distance, kinetic energy is being used in performing work.

[#565] For which of the following substances, the resistance decreases with increase in temperature?
Correct Answer

(B) Copper

Explanation

Solution: Option B: Copper (Correct Answer) Copper is an exception among common conductive materials. It has a negative temperature coefficient of resistance, meaning its resistance decreases as temperature increases. This unique property makes copper an excellent conductor of electricity and well-suited for applications where minimal resistance and efficient energy transmission are required. Option A: Pure silicon Silicon is a semiconductor material. In semiconductors like silicon, the resistance increases with an increase in temperature. This is due to the increased thermal generation of charge carriers (electrons and holes), which increases the conductivity and resistance. Option C: Nichrome Nichrome is a nickel-chromium alloy commonly used as a resistance wire in heating elements. It is known for its relatively high resistivity and stability at high temperatures. However, nichrome also exhibits a positive temperature coefficient of resistance, meaning its resistance increases with temperature. Option D: Platinum Platinum is a metal known for its excellent resistance to corrosion and high-temperature stability. However, like most metals, platinum exhibits a positive temperature coefficient of resistance. As temperature increases, the thermal vibrations of atoms within the metal lattice increase, causing greater scattering of electrons, which in turn increases resistance. In summary, the other options (pure silicon, nichrome, and platinum) all have materials with a positive temperature coefficient of resistance, meaning their resistance increases as temperature rises. Copper, on the other hand, exhibits a negative temperature coefficient of resistance, making it the correct choice for a substance in which resistance decreases with increasing temperature.