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De Broglie's identity gives the relationship between the momentum and the wavelength of a particle:

where
p is the particle momentum
m is its mass
v its velocity
h is the Planck constant

is the wavelength
By re-arranging the equation, we get

and by using the data about the proton, given in the text, we can find the proton's wavelength:
Angular acceleration = (change in angular speed) / (time for the change)
Change in angular speed = (ending speed) minus (starting speed)
Change in angular speed = (16 rad/s) - (zero) = 16 rad/s .
Angular acceleration = (16 rad/s) / (0.4 s)
(Average) angular acceleration = 40 rad/s²
Answer:
By convention a negative torque leads to clockwise rotation and a positive torque leads to counterclockwise rotation.
here weight of the child =21kgx9.8m/s2 = 205.8N
the torque exerted by the child Tc = - (1.8)(205.8) = -370.44N-m ,negative sign is inserted because this torque is clockwise and is therefore negative by convention.
torque exerted by adult Ta = 3(151) = 453N , counterclockwise torque.
net torque Tnet = -370.44+453 =82.56N , which is positive means counterclockwise rotation.
b) Ta = 2.5x151 = 377.5N-m
Tnet = -370.44+377.5 = 7.06N-m , positive ,counterclockwise rotation.
c)Ta = 2x151 = 302N-m
Tnet = -370.44+302 = -68.44N-m, negative,clockwise rotation.