Answer:
The time taken to stop the box equals 1.33 seconds.
Explanation:
Since frictional force always acts opposite to the motion of the box we can find the acceleration that the force produces using newton's second law of motion as shown below:

Given mass of box = 5.0 kg
Frictional force = 30 N
thus

Now to find the time that the box requires to stop can be calculated by first equation of kinematics
The box will stop when it's final velocity becomes zero

Here acceleration is taken as negative since it opposes the motion of the box since frictional force always opposes motion.
The line at the bottom of the picture ... probably the first line on a list of choices .. is the correct equation.
Answer:
the formulae is f = mg = vpg
To solve this problem we will apply the concepts related to the conservation of momentum. This can be defined as the product between the mass and the velocity of each object, and by conservation it will be understood that the amount of the initial momentum is equal to the amount of the final momentum. By the law of conservation of momentum,

Here,
= Mass of Basketball
= Mass of Tennis ball
= Initial velocity of Basketball
= Initial Velocity of Tennis ball
= Final velocity of Basketball
= Final velocity of the tennis ball
Replacing,

Solving for the final velocity of the tennis ball

Therefore the velocity of the tennis ball after collision is 11 m/s