Answer:
F = 51.3°
Explanation:
The component of weight parallel to the inclined plane must be responsible for the rolling back motion of the car. Hence, the force required to be applied by the child must also be equal to that component of weight:

where,
W = Weight of Wagon = 150 N
θ = Angle of Inclinition = 20°
Therefore,

<u>F = 51.3°</u>
The properties of the wave don't determine its speed. The properties of the medium do. You can FIND the speed by measuring the wave's frequency and wavelength.
The other 4 kg of mass may have departed the scene
of the fire, in the form of gases and smoke particles.
Answer:
Option E is correct.
There must be a horizontal wind opposite the direction of the stone's motion, because ignoring air resistance when calculating the horizontal range would yield a value greater than 32 m.
Explanation:
Normally, ignoring air resistance, for projectile motion, the range (horizontal distance teavelled) of the motion is given as
R = (u² sin 2θ)/g
where
u = initial velocity of the projectile = 20 m/s
θ = angle above the horizontal at which the projectile was launched = 30°
g = acceleration due to gravity = 9.8 m/s²
R = (30² sin 60°) ÷ 9.8
R = 78.53 m
So, Normally, the stone should travel a horizontal distance of 78.53 m. So, travelling a horizontal distance of 32 m (less than half of what the range should be without air resistance) means that, the motion of the stone was impeded, hence, option E is correct.
There must be a horizontal wind opposite the direction of the stone's motion, because ignoring air resistance when calculating the horizontal range would yield a value greater than 32 m.
Hope this Helps!!!