Answer:
A. Positive, positive
Explanation:
As we defined the ground is the origin, as long as the rock is above the ground, its position would always be positive.
As for velocity, as long as the rock is moving upwards, its direction is also upward, so its velocity is always positive. The velocity will become negative when the rock falls down.
Answer:
Wt = 26.84 [N]
Explanation:
In order to solve this problem we must use the definition of work in physics. Which tells us that this is equal to the product of force by distance.
In this case, we must sum the works of the force applied by the box and the friction force that also acts on the box.
The friction force is defined as the product of the normal force by the coefficient of friction.
f = N*μ
where:
N = normal force = m*g [N] (units of Newtons)
m = mass = 72 [kg]
g = gravity acceleration = 9.81 [m/s²]
f = friction force [N]
μ = friction coefficient = 0.21
f = 72*9.81*0.21
f = 148.32 [N]
Now the total work:
Wt = WF - Wf
where:
Wt = total work [J] (units of Joules)
WF = work by the pushing force [J]
Wf = work done by the friction force [J]
Wt = (160*2.3) - (148.32*2.3)
Wt = 26.84 [N]
Note: The friction force exerts a negative work, because this force is acting in opposite direction to the movement, therefore the negative sign.
A - the amount of time needed to travel the distance
The formula for speed is distance/time and the unit is m/s. Therefore you divide the distance travelled by the time it took to travel it.
Answer:
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Explanation:
