There is one major difference between electromagnetic waves and mechanical waves. Electromagnetic waves can travel through space and medium. Mechanical waves needs matter to transfer.
Given:
v(final velocity)= 7.5 m/s
t(time taken to pedal along)=4.5 s
Displacement (s)=19 m
Now we know that
s=ut+1/2(at^2)
Where s is the displacement measured in m
u is the initial velocity measured in m/sec
a is the acceleration measured in m/s^2.
t is the time taken to cover this distance.
Substituting the given values in the above formula we get
19= 4.5u+1/2(a x 4.5 x 4.5)
20.25 a + 9 u = 38
Now we also know that
v= u + at
Substituting the given values in the above formula we get
7.5= u + 4.5a
Solving for u and a from the above equations we get
u = 0.944m/s
a= 1.45 m/s^2
Thus the initial velocity is 0.944 m/s
The work done on the bullet is force•distance. This is also equivalent to the energy it has leaving the muzzle (work energy theorem). This kinetic energy is (1/2)(0.006kg)(336m/s)^2=338.7J. Then 338.7J=F•0.83m
F=338.7/0.83=408N
because of gravitional pull