Answer:
A) s=1/2at^2
t=√(2s/a)=√(2x400)/10.0)=9.0s
B) v=at
v=10.0x9=90m/s
Answer:

Explanation:
Maximum height of the pumpkin, 
Initial speed, v = 22 m/s
We need to find the angle with which the pumpkin is fired. the maximum height of the projectile is given by :

On rearranging the above equation, to find the angle as :



So, the angle with which the pumpkin is fired is 39.49 degrees. Hence, this is the required solution.
Answer:
n=6.56×10¹⁵Hz
Explanation:
Given Data
Mass=9.1×10⁻³¹ kg
Radius distance=5.3×10⁻¹¹m
Electric Force=8.2×10⁻⁸N
To find
Revolutions per second
Solution
Let F be the force of attraction
let n be the number of revolutions per sec made by the electron around the nucleus then the centripetal force is given by
F=mω²r......................where ω=2π n
F=m4π²n²r...............eq(i)
as the values given where
Mass=9.1×10⁻³¹ kg
Radius distance=5.3×10⁻¹¹m
Electric Force=8.2×10⁻⁸N
we have to find n from eq(i)
n²=F/(m4π²r)

Greek philosophers Leucippus and Democritus first developed the concept of the atom in the 5th century B.C.E.