You have been moving a 43 lb sack across the floor with the constant velocity of

Question

You have been moving a 43 lb sack across the floor with the constant velocity of 0.43 m/s, by applying a steady horizontal force of 8.7 N. You've pulled the sack a little harder, and managed to get the sack moving faster. What is the magnitude of the force that you need to be applying to the sack to keep it moving at the increased speed of 0.76 m/s? John was pushing a 24.7 kg box horizontally with a force of 2.7 N at a steady speed of 0.2 m/s. Then he decided to tie a rope to the box to make it possible to pull it forward. Now the box is moving at 0.6 m/s as John is pulling on it at the angle of 29.9 degree up of horizontal. What is the magnitude of the force of John's pull?

Explanation / Answer

1)

when velocity increases t0 a constant velocity the applied force must be same as frictional force

in the first case the object moves in constant velocity

so the frictional force is 8.7N

so when velocity increases to a constant value of 0.76m/sec then the force must be equal to frictional force to keep it in constant value

so the answer is

F=8.7N

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

force=2.7cos29.9

f=2.34N

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