Consider a large truck carrying a heavy load, such as steel beams. A significant hazard for the driver is that the load may slide forward, crushing the cab, if the truck stops suddenly in an accident or even in braking. Assume, for example, that a 10,000 kg load sits on the flat bed of a 25,000 kg truck moving at 14.0 m/s. Assume that the load is not tied down to the truck, but has a coefficient of friction of 0.400 with the flat bed of the truck.Calculate the minimum stopping distance for the truck for which the load will not slide forward relative to the truck.

Respuesta :

Answer:

25 m

Explanation:

The maximum acceleration that the load can withstand without slipping out of the truck occurs when the net force on the load is equal to the maximum frictional force, therefore:

[tex]ma_{max} =-\mu N[/tex]

where

m = 10,000 kg is the mass of the load

[tex]a_{max}[/tex] is the maximum acceleration

[tex]\mu = 0.400[/tex] is the coefficient of friction

N is the reaction force of the truck on the load

Since the surface is horizontal, the reaction force is equal to the weight of the load, [tex]N=mg[/tex], so from the previous equation we get

[tex]a_{max} = -\mu g = -(0.400)(9.8)=-3.92 m/s^2[/tex]

where the sign is negative since the direction of the acceleration is opposite to the motion of the truck.

At the maximum acceleration, the stopping distance of the truck is the minimum. Therefore, we can use the SUVAT equation:

[tex]v^2-u^2 = 2a_{max} d[/tex]

where

v = 0 is the final velocity of the truck

u = 14.0 m/s is the initial velocity

d is the minimum stopping distance

Solving for d, we find

[tex]d=\frac{-u^2}{2a_{max}}=\frac{-(14)^2}{2(-3.92)}=25 m[/tex]