Answer:
If the system consists of the block only, the work done by the gravity is negative.
If the system consists of the block and the earth the work done by the gravity is zero.
Explanation:
If the system consists of the block only, then the system experiences two external forces: one exerted by the hand that lifts the block vertically upward and other exerted by the earth (gravity), which is opposed to the movement of the system, so the work done by gravity is negative.
On the other hand, if the system consists of the block and the earth, then only exists a external force which is the exerted by the hand. So, the force exerted by gravity is zero.
Answer:

Explanation:
given,
traffic light weight = 100 N
angle at which the rope is supported = 30°
vertical component of force = ?







Step 1: Look in your book or online for the conical pendulum equation.
Step 2: Look at the drawing and see which angle is involved in the equation.
Answer: It's Angle #2 in your drawing.
Answer: Third option
F = 250w
Explanation:
The impulse can be written as the product of force for the time interval in which it is applied.

You can also write impulse I as the change of the linear momentum of the ball

So:

We want to find the force applied to the ball. We know that
milliseconds = 0.03 seconds
The initial velocity
is zero.
The final speed 
So


We must express the result of the force in terms of the weight of the ball.
We divide the expression between the acceleration of gravity


The answer is the third option