The third option is wrong
Is there any chemical names listed ?
Answer:
the work done by the 30N force is 4156.92 J.
For this problem, they don´t ask you to determine the work of the total force applied in the block. They only want the work done for the force of 30N, with an angle of 30º respectively of the displacement and a traveled distance of 160m. So:
W=F·s·cos(α)=30N·160m·cos(30º)=4156.92J
5 seconds is a poor time to ask about, because the speed abruptly changes at exactly 5 seconds.
Up until that time, the speed has been 1 m/s. And then, at exactly 5 seconds, it becomes zero.
_________
It's also a poor question because speed is calculated from the distance covered, but the graph shows displacement, not distance. You can't really tell the distance covered from a displacement graph.
For example, if an object happens to be moving in a circle around the place where it started, then the total distance covered keeps increasing, but its displacement is constant.
Answer:
Yes, if the system has friction, the final result is affected by the loss of energy.
Explanation:
The result that you are showing is the conservation of mechanical energy between two points in the upper one, the energy is only potential and the lower one is only kinetic.
In the case of some type of friction, the change in energy between the same points is equal to the work of the friction forces
= ΔEm
=
-Em₀
As we can see now there is another quantity and for which the final energy is lower and therefore the final speed would be less than what you found in the case without friction.
=
+ Em₀
Remember that the work of the rubbing force is negative, let's write the work of the rubbing force explicitly, to make it clearer
½ m v² = -fr d + mgh
v = √(-fr d 2/m + 2 gh)
v = √ (2gh - 2fr d/m)
Now it is clear that there is a decrease in the final body speed.
Consequently, if the system has friction, the final result is affected by the loss of energy.