Answer:

Explanation:
We need only to apply the definition of acceleration, which is:

In our case the final velocity is
, the initial velocity is
since it departs from rest, the final time is
and the initial time we are considering is 
So for our values we have:

Power = work/time
= 500/10
= 50J/s or 50 watt
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:
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Answer:
The magnitude of the rate of change of the child's momentum is 794.11 N.
Explanation:
Given that,
Mass of child = 27 kg
Speed of child in horizontal = 10 m/s
Length = 3.40 m
There is a rate of change of the perpendicular component of momentum.
Centripetal force acts always towards the center.
We need to calculate the magnitude of the rate of change of the child's momentum
Using formula of momentum


Put the value into the formula


Hence, The magnitude of the rate of change of the child's momentum is 794.11 N.