One light-year is the distance that light travels in vacuum
in one year. It's a unit of distance.
Newton's second law states that the resultant of the forces applied to an object is equal to the product between the object's mass and its acceleration:

where in our problem, m is the mass the (child+cart) and a is the acceleration of the system.
We are only concerned about what it happens on the horizontal axis, so there are two forces acting on the cart+child system: the force F of the man pushing it, and the frictional force

acting in the opposite direction. So Newton's second law can be rewritten as

or

since the frictional force is 15 N and we want to achieve an acceleration of

, we can substitute these values to find what is the force the man needs:
Answer:
0.84 s
Explanation:
Step 1
Given information:
Mass of the ice (m) = 2.0 kg
Heat transfer rate (Q/T) = 793.0 kW
Latent heat of fusion of ice (Lf) = 334 kJ/kg

Substituting the corresponding values we have:
