A student pulls a block over a rough surface with a constant force FP that is at an angle θ above the horizontal, as shown above
. If FP remains constant but the angle θ is increased, which of the following is true at some later time?
A.The force of friction between the block and surface will increase.
B.The force of friction between the block and surface will decrease.
C.The weight of the block will increase.
D.The weight of the block will decrease.
A.The force of friction between the block and surface will increase.
B.The force of friction between the block and surface will decrease.
C.The weight of the block will increase.
D.The weight of the block will decrease.
2 answers:
Response:
B. The friction force between the block and surface will diminish.
Clarification:
The force of friction can be expressed as
where represents the friction coefficient and
signifies the normal force.
As the student pulls the block with force at an angle
, the normal force acting on the block subsequently becomes
and therefore, the frictional force changes to
.
With an increase in , the
increases, which subsequently reduces the normal force
, indicating a decrease in the frictional force; hence choice B is correct.
Note: While choice D seems appealing, it is incorrect since the weight remains unaffected by the external forces acting on the block.
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with initial velocity u = 0. Substituting a1 and t1 gives:
Afterward, the rocket decelerates uniformly at
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and knowing , solve for t2, the time until the rocket halts:
2) 299.9 m
Calculate distances covered in both phases.
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Substituting values from part 1,
Distance in the deceleration phase:
Substituting known values,
Total distance traveled is
d = 82.7 m + 217.2 m = 299.9 m