PY H3:

1)

When you apply a horizontal force of 44 N to a block, the block moves across the floor at a constant speed (,uk = #5). (a) What happens if instead you apply a force of 35 N to the block initially at rest? The block decelerates (the speed continually decreases). The block doesn't move. The block moves at a constant speed, but it moves more slowly. (b) when you apply a force of 35 N to the block initially at rest, what is the magnitude of the horizontal component of the force that the floor exerts on the block? Fhor = N (c) What happens if instead you exert a force of 50 N? The block accelerates (the speed continually increases). The block doesn't move. The block moves at a constant speed, but it moves faster. (d) When you apply a force of 50 N, what is the magnitude of the horizontal component of the force that the oor exerts on the block? thr = N Bob is pushing a box across the floor at a constant speed of L8 m/s, applying a horizontal force whose magnitude is 55 Ni Alice is pushing an identical box across the floor at a constant speed of 3.6 m/s, applying a horizontal force (a) What is the magnitude of the force that Alice is applying to the box? F = N (b) With the two boxes starting from rest, explain qualitatively what Alice and Bob did to get their boxes moving at different constant speeds. In order to keep the box moving twice as fast, Alice had to apply a constant force that was twice as large as the force that Bob applied. Each initially applied a force bigger than static friction to get the box moving and accelerating, then when the desired nal speed was achieved they reduced the force to make the net force zeroi A 21 kg box sits on a table. The coefficient of static friction #5 between table and box is 0.25, and the coefficient of kinetic friction [4k is 0.22. (a) What is the force required to start the box moving? F = N (b) What is the force required to keep it moving at constant speed? F = N A 8 kg box with initial speed 5 m/s slides across the oor and comes to a stop after 1.4 s. (a) What is the coefficient of kinetic friction? #k = (b) How far does the box move? distance = m (c) You put a 4 kg block in the box, so the total mass is now 12 kg, and you launch this heavier box with an initial speed of 5 m/s. How long does it take to stop? At = s A 22 kg box is being pushed across the floor by a constant force N. The coefficient of kinetic friction for the table and box is 0.15. At t = 7.0 s the box is at location m, traveling with velocity m/s. What is its position and velocity at t = 8.3 s? New velocity V = n/s New position d m