Answer:
4.28 s
Explanation:
after two seconds (2 s) His friends is
d = 3.5 m/s x 2 s = 7 meter ahead.
in this state, a bicylist start from initial velocity vo = 0 m/s and accelerat 2.4 m/s²
then, when bicylist reach his friend
t friend = t bicyclist = t
d bicylist = d friend + d
-------
d friend = 3.5 . t
d bicylist = vo . t + ½ a t²
d friend + d = vo . t + ½ a t²
3.5 t + 7 = 0 . t + ½ . 2.4 . t²
3.5 t + 7 = 1.2 t²
0 = 1.2 t² - 3.5 t - 7
t = -1.363 and t = 4.28
take the positive one
The distance covered by the proton is 48.4 m
Explanation:
The electric field produced by an electrically charged infinite plane is given by

where in this case,
is the surface charge density
is the vacuum permittivity
Substituting,

And the direction is towards the plane (because the charge is negative).
The electric force on the proton due to this field is

where
is the proton charge
Substituting,

where the direction is toward the plane.
Now we can calculate the proton's acceleration using Newton's second law:

where
is the proton mass
Substituting,

Now we can finally apply the following suvat equation for accelerated motion to find the distance travelled by the proton:

where
v = 0 is the final velocity
is the initial velocity
a is the acceleration
s is the distance covered
And solving for s,

Therefore, the closest answer is 48.4 m.
Learn more about accelerated motion:
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Answer: "For a projectile with no air resistance, at the peak of its path, it's velocity is equal to zero"
Explanation:
Suppose that you throw an object up. The initial vertical velocity will be positive, and the acceleration (the gravitational acceleration) will point downwards, meaning that it opposes to the initial direction of the velocity, and that decreases the velocity as the time goes by.
There will be a point where the velocity ( that was positive until now, so until now the height of the object was increasing), is equal to zero, this means that at this moment the object stops moving, and after, because we still have negative acceleration, the velocity will start become negative, and the object will fall down.
Then that point where the velocity was zero is the peak of its path, then we can conclude that:
"For a projectile with no air resistance, at the peak of its path, it's velocity is equal to zero"