C. copper
Explanation:
Copper is the best conductor of heat from the given options. Plastic, wood and cotton are all poor conductors other wise known as insulators.
Metals are typically good conductors of heat.
- they generally do not have a high specific heat capacity which implies that they get heated easily.
- a good conductor allows heat to flow fast and it simultaneously loses heat readily too.
- copper is a good conductor, when heat its perfectly allows heat to pass through
- when heat is removed, it loses it very fast.
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The time period of the pendulum is affected by the acceleration due to gravity. The tension does not have any effect on the time period of the pendulum and also the mass of the bob does not effect the time period of the pendulum.

Hence, if the gravity increases then the time period of the pendulum will decreases and it will swing faster.
Answer:
options A and C
Explanation:
Since, the spheres are of same size and rotational speed of the sphere are not dependent on their masses. So, both the sphere will reach the bottom of the at the same time with the same speed. But their kinetic energies are different.
So, options A and C are correct.
Answer:
9.75 x 10^4 J
Explanation:
Work done, W = 9.75 x 10^4 J
According to the work energy theorem, the change in kinetic energy is equal to the work done by all the forces.
So, here work done is 9.75 x 10^4 J so the change in kinetic energy is 9.75 x 10^4 J.
Answer:
1.1397 Nm
Explanation:
When the palmaris longus muscle in the forearm is flexed, the wrist moves back and forth.
If the muscle generates a force
and
, then the torque is equal to 
we see that r = 2.65 cm = 0.0265 m
therefore
torque = 0.0265 x 49.5
= 1.1397 Nm