It's average speed during that 26 seconds was about 4.77 m/s. Without seeing the graph, we can't tell if it was going faster or slower at any particular time during that period. All we can tell is its average for the full interval.
Answer:
16.63min
Explanation:
The question is about the period of the comet in its orbit.
To find the period you can use one of the Kepler's law:

T: period
G: Cavendish constant = 6.67*10^-11 Nm^2 kg^2
r: average distance = 1UA = 1.5*10^11m
M: mass of the sun = 1.99*10^30 kg
By replacing you obtain:

the comet takes around 16.63min
The equation for the de Broglie wavelength is:
<span>λ = (h/mv) √[1-(v²/c²)], </span>
<span>where h is Plank's Constant, m is the rest mass, v is velocity, and c is the velocity of light in vacuum. However, if c>>v (and it is, in this case) then the expression under the radical sign approaches 1, and the equation simplifies to: </span>
<span>λ = h/mv. </span>
<span>Substituting, (remember to convert the mass to kg, since 1 J = 1 kg·m²/s²): </span>
<span>λ = (6.63x10^-34 J·s) / (0.0459 kg) (72.0 m/s) = 2.00x10^-34 m.</span>