Download Forces, Gravity, Friction and Newton`s Laws Test: Practice problems

Forces, Gravity, Friction and Newton’s Laws Test:
Practice problems and answers.
1. Please describe the action and reaction forces involved in spiking a
volleyball. Remember when you describe the action and reaction forces
you must identify the object exerting the force and the object
receiving the force. 2. Also explain the effect of the action and reaction forces.
Answer 1:
When you spike a volleyball, your hand is hitting the volleyball and the
volleyball returns the force to your hand. The forces from your hand and
from the ball are exactly equal and in opposite directions.
If the action force was your hand hitting the ball then it would cause
the ball to move quickly downward. The reaction force from the ball back
onto the hand would cause your hand to slow down (decelerate) during the
swing.
Answer 2:
The action reaction forces involved in hitting a volleyball are between
the hand and the ball. They cause the ball to be spiked.
Answer 3:
The action force is the hand hitting the ball, forcing it down.
Answer 4:
Action and reaction forces are opposite. They cancel each other out
they come from the ball and the hand when the hand hits the ball it makes
the ball move when the hand hits the ball the ball hits the hand this makes
the hand move too.
(Only answer # 1 would receive full points. #4 contains the basic ideas, but
is unclear, doesn’t define the forces well and uses a run-on sentence. #2
and 3 are both very incomplete.)
What forces are acting on you when you slide down the banister of a staircase. (A banister
is a railing.) Are the forces balanced or unbalanced? How do you know?
The forces acting on you when you slide down a banister must be unbalanced. I know this
because when I slide down, I accelerate and the only way an object accelerates is with an
unbalanced force. The force of sliding friction is fighting against my sliding motion, but the
force of gravity pulling me down is greater.
What could you do to reduce the friction between yourself and the banister?
I could make both surfaces smoother, maybe by wearing pants with slippery fabric or
waxing or greasing the banister. I could possibly also use something round to roll down the
banister since rolling friction would be less than sliding friction. If I could put a layer of air
or water between me and the banister then the friction would really be reduced because
fluid friction could be even less than sliding and rolling friction.
There is gravity between you and the Earth. Weight is a measurement of that gravity.
What happens to your weight when you gain mass? What would happen to your weight if
the Earth gained mass?
If I gained mass, I would weight more. This is because there would be more of me for the
Earth to pull on. If the Earth gained mass, I would still weigh more; there would be more of
the Earth for me to pull on. I attract the Earth and it attracts me because of gravity.
Santa’s reindeer were having a competition over who could pull the most toys in a sleigh.
Dasher and Dancer competed against each other in a pulling contest. Dancer was
victorious. Give two possible reasons why Dancer won the contest using Newton’s second
law.
1. Dancer could have accidentally had a sleigh with fewer toys. Less mass in his sleigh
would mean more acceleration of the sleigh even if he could only pull with the same
force as Dasher.
2. Dancer could have been a bit stronger than Dasher. If their sleighs weighed the
same and Dancer pulled with more force, then his sleigh would accelerate at a
higher rate.