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:
The kinetic energy of the system after the collision is 9 J.
Explanation:
It is given that,
Mass of object 1, m₁ = 3 kg
Speed of object 1, v₁ = 2 m/s
Mass of object 2, m₂ = 6 kg
Speed of object 2, v₂ = -1 m/s (it is moving in left)
Since, the collision is elastic. The kinetic energy of the system before the collision is equal to the kinetic energy of the system after the collision. Let it is E. So,

E = 9 J
So, the kinetic energy of the system after the collision is 9 J. Hence, this is the required solution.
Answer:
Coefficient of static friction will be equal to 0.642
Explanation:
We have given acceleration 
Acceleration due to gravity 
We have to find the coefficient of static friction between truck and a cabinet will
We know that acceleration is equal to
, here
is coefficient of static friction and g is acceleration due to gravity
So 
So coefficient of static friction will be equal to 0.642
Check the attached file for the answer.
Friction between the ball and the floor is stealing some of the kinetic energy of the ball, and turning it into heat.