Your weight pushing down on the chair is the action force. The reaction force is the force exerted by the chair that pushes up on your body.
Time period = time/no. of waves = 6/3 = 2s
Answer:

Explanation:
From the question we are told that:
Force P=88Ib
Mass of crate M_c=210Ib
Generally the equation for Frictional force F is mathematically given by


with 

Therefore since Static Friction supersedes applied force body remains at rest.
Frictional force =88Ib (negative)

Answer:
x = 5.29 m
Explanation:
given,
weight of stretch = 37 N
left-hand spring constant (k₁)= 2.7 N/cm
right hand spring constant(k₂)= 4.3 N/ cm
spring are connected in parallel
F = F₁ + F₂
F = k₁x + k₂x
F = (k₁+ k₂)x
37= (4.3+ 2.7)x
7 x = 37
x = 5.29 m