Arrestor beds are used to help moving trucks to come to a stop when their brakes fail.
The driver of a 30 000 kg truck driving down a steep road drives onto an ASCENDING arrestor bed inclined at 28° to the horizontal, as shown in the diagram below.
5.1 State the work-energy theorem in words. (2)
The truck with failed brakes passes point A at the beginning of the arrestor bed at a speed of 33 m∙s-1.
The average frictional force on the truck is 31 000 N while the truck moves up the arrestor bed.
Ignore the rotational effects of the wheels.
5.2 Give a reason why the net work done on the truck, while moving on the
arrestor bed, is negative. (1)
5.3 Use ENERGY PRINCIPLES to calculate the minimum length of the arrestor
bed needed to bring the truck to a stop. (5)
The diagram below shows the same truck entering a DESCENDING arrestor bed inclined at 28° to the horizontal. The initial speed of the truck and the average frictional force on the truck are 33 m∙s-1 and 31 000 N respectively.
5.4 Which arrestor bed, ASCENDING or DESCENDING, will be able to stop the truck in a shorter distance?
Explain the answer in terms of the forces acting on the truck. (3)
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