Answer:
Explanation:
It's equal to change of momentum in contact
The force exerted on the box is 56 N
Explanation:
The work done by a force on an object is given by

where
F is the magnitude of the force
d is the displacement of the object
is the angle between the direction of the force and of the displacement
For the box in this problem, we have:
W = 2240 J is the work done
d = 40 m is the displacement of the box
Assuming that the force is parallel to the displacement, 
Solving the equation for F, we find the force exerted on the box:

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Answer:
what?
Explanation:
does that means also i learned Ratios and multiplication i keared them like 5 years ago?
Answer:
The magnitude of the force between the two parallel wires is 0.0111 N.
Explanation:
Given;
length of the two parallel wires, L = 42 m
distance between the two wires, r = 0.03 m
current in both wires, I₁, I₂ = 6.3 A
Therefore, the magnitude of the repulsive force between the two parallel wires is given by;

Therefore, the magnitude of the force between the two parallel wires is 0.0111 N.
The initial kinetic energy of the boat and its rider is

After Sam stops it, the final kinetic energy of the boat+rider is

because its final velocity is zero.
For the law of conservation of energy, the work done by Sam is the variation of kinetic energy of the system:

where the negative sign is due to the fact that the force Sam is applying goes against the direction of motion of the boat.