Answer: Friction
Explanation:
The friction force is the force exerted by a surface as an object moves across it or makes an effort to move across it. There are at least two types of friction force - sliding and static friction. Though it is not always the case, the friction force often opposes the motion of an object.
Answer:

Explanation:
Friction force to find the speed of the block at the instant of collision so







Solve to v' to find the velocity


The speed of the block at the instant of collision with the spring is

The potato reach a velocity of 0 m/s after 3.57 s
Explanation:
There is only one force acting on the potato, which is in free fall: the force of gravity, acting downward. Therefore, the motion of the potato is a free fall motion with constant acceleration equal to the acceleration of gravity, and we can use the suvat equation:

where
v is the final velocity
u is the initial velocity
is the acceleration of gravity (negative since downward)
t is the time
For the potato in this problem:
u = +35 m/s
So the time t at which the velocity reaches
v = 0
is

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Part A)
As we know that spring force is given by
F = kx
here x = stretch in the spring from natural length
So here when spring reaches to its natural length
Force due to spring = 0
so acceleration = 0
Part b)
When spring is compressed from its natural length it will have elastic potential energy in it
so it is given by

now we know that there is no friction in it so maximum kinetic energy of the launcher must be equal to the elastic potential energy of the spring

here we have
k = 70 N/m
x = 0.4 m


Part c)
Now to find the speed we know that



so its speed is 6.11 m/s