My guesses would be g. or F
"Constant velocity" is another way of saying "zero acceleration".
Answer:
17.6 N
Explanation:
The force exerted by the punter on the football is equal to the rate of change of momentum of the football:

where
is the change in momentum of the football
is the time elapsed
The change in momentum can be written as

where
m = 0.55 kg is the mass of the football
u = 0 is the initial velocity (the ball starts from rest)
v = 8.0 m/s is the final velocity
Combining the two equations and substituting the values, we find the force exerted on the ball:

Answer:
a. stay the same for very long
Explanation:
It is rare for any motion to stay the same for a very long time. The force applied on a body causes changes in the magnitude of motion.
- For motion to remain constant, there must not be a net force acting on the body
- All the forces on the body must be balanced.
- This is very hard to come by.
- Motion changes very frequently.
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: