A device used to measure atmospheric pressure is a barometer.
Answers:
a) 10 m
b) time=1.6 s, frquency=0.625 Hz
c) 6.25 m/s
Explanation:
a) If there is a crest at each dock and another three crests between the two docks, and the wavelength
is the distance between to crests; this means we have
in
:

Clearing
:


b) This part can be solved by a Rule of Three:
If 10 waves ---- 16 s
1 wave ----- 
Then:

This is the period of the wave
On the other hand, the frequency
of the wave has an inverse relation with its period
:


This is the frequency of the wave
c) The speed
of a wave is given by the following equation:


Finally:

For this case we first think that the skateboard and the child are one body.
We have then:
1 = jug
2 = skateboard + boy
By conservation of the linear amount of movement:
M1V1i + M2V2i = M1V1f + M2V2f
Initial rest:
v1i = v2i = 0
0 = M1V1f + M2V2f
Substituting values
0 = (7.8) (3.2) + (M2) (- 0.65)
0 = 24.96 + M2 (-0.65)
-24.96 = (-0.65) M2
M2 = (-24.96) / (- 0.65) = 38.4 kg
Then, the child's mass is:
M2 = Mskateboard + Mb
Clearing:
Mb = M2-Mskateboard
Mb = 38.4 - 1.9
Mb = 36.5 Kg
answer:
the boy's mass is 36.5 Kg
Missing figure and missing details can be found here:
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Solution:
(a) The work done by the spring is given by

where k is the elastic constant of the spring and

is the stretch between the initial and final position. Since x1=-8 in=-0.203 m and x2=5 in=0.127 m, we have

(b) The work done by the weight is the product of the component of the weight parallel to the inclined plane and the displacement of the cart:

where the negative sign is given by the fact that

points in the opposite direction of the displacement of the cart, and where

therefore, the work done by the weight is