Force and Motion Common Unit Assessment
The distance an object travels per unit of time.
Speed = distance /time
Example problem: A blue dolphin swims 120 km in 6 hours. What is the dolphin’s speed?
Show your work and label your answer.
120 km/6 hr= 20 km/hr
What is relative motion? How do you know if something or someone is in motion relative to an
lative motion is motion compared to a reference point
An object is in m
otion relative to an object if it’s position
and/or direction) from the object has changed.
Example Question: You are riding in a car going to school. Are you in motion rela
tive to the car?
Yes or No. Explain.
in motion relative to the car because the distance between
you and the car has not changed.
Are you in motion relative to the school? Yes or No. Explain.
in motion relative to the school because the distance between
you and the school is changing.
Define buoyant force.
Buoyant force is an upward force applied by a fluid on an object in the
Explain each scenario (Ascend, Hover and Sink) in terms of buoyant force and weight. Also,
explain why the object will sink, hover or ascend.
An object will ascend (rise) if the buoyant force is greater than the
object’s weight (or the object’s weight i
s less than the buoyant force.
An object will hover (neither rise nor sink) if the buoyant force is equal
to the object’s weight
An object will sink if the buoyant force is less than the object’s weight
(or the object’s weight is greater than the buoyant f
Example Problem: If an object is hit with a 20 N force from the left
and 35 N force from the right,
in which direction will the object travel, and what is its net force? Include diagram!
Net force = 15 N left
A block of wood is at rest on a wooden ramp. Draw arrows and label the forces acting on the
It is fine, but not necessary to
have Fn. Fg
and Ff should be the same length.
When wheels are attached to the block of wood, it moves down the ramp. Draw arrows and label
the forces acting on the block.
It is fine, but not necessary to have Fn.
Fg should be vi
sibly longer than Ff.
Explain how the motion of the wooden block is affected by the balanced/unbalanced forces you
labeled in the diagrams above.
Figure # 10
the block is not in motion because the forces of gravity
and friction are balanced
or the net force = 0.
Figure # 11
the block is rolling down the ramp because the force of
gravity is greater than the force of friction
the net force does not =
or the forces are unbalanced.
A magazine is sitting on the dash board of a
car that is stopped at a traffic light. As the car starts
to move forward, the magazine slides backward off the dashboard. Use the term
The magazine is sitting still with the car at the stop light. When the car
to move, the force of the car acts on the car, but not on the
magazine. The inertia of the magazine make it resist moving, which
makes it stay in place. This causes it to slide off the dashboard.
Explain if work is being done in each example. Why or W
Leaning on a wall
is being done
a force is being exerted, bu
t is not causing the
wall to move in the direction of the force.
Lifting a back pack from the floor to a desk
Work is being done
the force is making the backpack move a distanc
in the same direction.
Ben lifts a crate straight up into a truck. Michael pushes an identical crate up a ramp into the
same truck. Assuming there is no friction; compare the amount of work done by Ben to the
amount of work done by Alex. Explain.
th men do the same amount of work. This is because the amount of
work done doesn’t change with or without a simple machine (if there
is no friction)
In a simple machine without friction there would be
Less input work than output work
Greater input wor
k than output work
Greater output work than input work
Equal input work and output work