Answer:
, assuming that the gravitational field strength is 
.
Explanation:
Notice that both the speed and the direction of motion of this block are constant. In other words, the velocity of this block is constant.
By Newton's Second Law, the net force on this block would be 
. External forces on this block should be balanced. Thus, the magnitude of the (downward) weight of this block should be equal to the magnitude of the (upward) force that the boy applies on this block.
Let 
denote the mass of this block. It is given that 
. The weight of this block would be:
.
Hence, the force that the boy applies on this block would be upward with a magnitude of 
.
The mechanical work that a force did is equal to the product of:
- the magnitude of the force, and
- the displacement of the object in the direction of the force.
The displacement of this block (upward by 
) is in the same direction as the (upward) force that this boy had applied. Thus, the work that this boy had done would be the product of:
- the magnitude of the force that this boy exerted, , and
- the displacement of this block in the direction, .
.
Answer:
Explanation:
according to Newton First Law of Motion (Law of Inertia); An object at rest will stay at rest, forever, as long as nothing pushes or pulls on it. An object in motion will stay in motion, traveling in a straight line, forever, until something pushes or pulls on it.
the marble will move in a straight line
The work-energy theorem states that the change in kinetic energy of the particle is equal to the work done on the particle:
The work done on the particle is the integral of the force on dx:
So, this corresponds to the change in kinetic energy of the particle.
