A spaceship located in deep space fires its rockets for 10 s,
after which the thrust is turned off. Compare the velocity of the
spaceship just after the rockets are turned off to its velocity one
minute later.
Once the rockets are turned off, the rocket
experiences no net force. So the velocity will remain the
same.
A block is sitting on a tabletop when a hand pushes it, giving it
an initial velocity v. The block slides across the table before
coming to rest. Draw a vector representing the net force on the block
for each of the following times:
a. As the hand is in contact with the block.
b. While the block is sliding across the table.
c. A few moments after the block has stopped sliding
a: While the hand is in contact with the
block it is accelerating to the right, so the net force must point in
that direction.
b.: As the block slides along the table,
friction slows it down, so the net force must point in the direction
opposite its velocity.
c: Since the block has stopped sliding, it
is no longer accelerating. Thus the net force is zero.
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