Answer:
A. The athlete isn’t doing any work because he doesn’t move the weight.
Explanation:
We must remember the definition of work, which says that work is equal to the product of mass by the distance displaced. In this case, the athlete only does work when he lifts the weight from the ground to the point where he holds the weight suspended.
So when he's holding the weight, he doesn't do any work.
Answer:
Smallest drop: Water
Largest drop: Dirt
Explanation:
The heat needed to change the temperature of a sample is:
(1)
with Q the heat (added(+) or removed(-)), c specific heat, m the mass and 
the change in temperature of the sample. So, if we solve (1) for
Sample A:
Sample B:
Sample C:
Note that the numbers 16744, 5400, 9450 are in the denominator of the expression 
that gives the drop on temperature. so, if Q is the same for the three samples the smallest denominator gives the largest drop and vice versa.
So, the smallest drop is Sample A and the largest is Sample C.
(Important: The minus sign of implies the temperature is dropping)
Answer:
Centripetal force is the force that keeps the yoyo going in a circle, if the string breaks, the yoyo would would fly off in a direction that is different to the point on the circle.
Just remember
Voltage = current times resistance
current = voltage over resistance
Current = 9/3 = 3
