If the sign of work is negative, that means the force and the motion are in opposite directions.
Let's say you see something roll off of the shelf. You catch it, and you let it down slowly and gently.
Gravity exerted down-force on it and it moved down. Gravity did positive work on it.
YOU exerted UP-force on it and it moved down. YOU did negative work on it.
(Also, the falling object exerted down-force on your hand, and your hand moved down. The falling object did positive work on your hand ! Where did THAT energy come from ? It came from the potential energy that the object had while it was on the shelf. Your hand absorbed that energy on the way down, doing negative work. So the object didn't have any kinetic energy when it reached the floor, and it did NOT splinter the floor or shatter in smithereens. It had barely enough energy left to make a sound when it hit the floor.)
The given question is incomplete. The complete question is as follows.
Measurements show that the enthalpy of a mixture of gaseous reactants decreases by 338 kJ during a certain chemical reaction, which is carried out at a constant pressure. Furthermore, by carefully monitoring the volume change it is determined that 187 kJ of work is done on the mixture during the reaction. Calculate the change in energy of the gas mixture during the reaction. Be sure your answer has the correct number of significant digits. Is the reaction exothermic or endothermic ?
Explanation:
The given data is as follows.
Change in enthalpy (
) = -338 kJ (as it is a decrease)
Work done = 187 kJ,
Change in energy (
) = ?
Now, according to the first law of thermodynamics the formula is as follows.
Hence, putting the given values into the above formula as follows.
Also, we know that W = 
so, 
= -151 kJ
Thus, we can conclude that the change in energy of the gas mixture during the reaction is -151 kJ.
Answer:
The elements in group 2 form compounds consisting of one atom of the element and two atoms of hydrogen: These are called alkaline earth metals, with similar properties among members of that group.
Explanation:
Answer:
b. an electric current is used to turn the pointer of a galvanometer
Explanation:
well , galvanometer is an important device which is used to detect an electric current through a conductor or circuit.
something special about it is that it can detect very minute current too
Answer:
4.465 m
Explanation:
Taken the beam to be uniform, then the center of gravity will act at the mid-point of the beam. The mid point = 11 / 2 = 5.5 m
since the boy can walk to the end of the beam without falling,
then the torque ( moment of the force) by beam = torque by students at the end of the beam
let the distance of the boy = x
220 ( 5.5 - x ) = 51 × x
1210 - 220 x = 51 x
1210 = 51 x + 220 x
1210 = 271 x
x = 1210 / 271 = 4.465 m
