Transcript Forces and Newton*s Laws: Practice

Forces and Newton’s Laws:
Practice
Once again: everybody fights,
nobody quits
Problem 1: OMG, they are so easy
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Newton’s 1st law:
Newton’s 2nd law:
Newton’s 3rd law:
What is difference between mass and weight?
…And then…
• An airplane is flying at a constant speed. Draw
a free body diagram of the plane below and
include all the forces on the plane.
…And then…
• A frisbee has been thrown and is maintaining
a constant altitude. Draw a free body diagram
below and show all the forces acting on the
frisbee.
…And then…
• A force of 20 N is acting at an angle of 500
from the horizontal.
• Find FX:
• Find FY:
…And then…
• A force of 30 N is acting at an angle of 1500
from the horizontal.
• Find FX:
• Find FY:
…And then…
• A pair of Freedom HS students find
themselves having to push a stalled car.
Frances Lee pushes with a force of 400 N and
Kyle Cogar pushes with a force of 300 N. There
is a 590N frictional force acting on the car.
• Draw a free body diagram for the system.
• Find the acceleration.
• a = 0.059m/s2
…And then…
• Jordan Lee is on a raft. He exerts a force of
17N due east by rowing and the current exerts
a force of 15 N at 670. Ignoring friction, what
are the X- and Y-components of the raft’s
acceleration if the total mass = 1300Kg?
• aX = 0.018m/s2, aY = 0.011m/s2
• Total magnitude of acceleration?
…And then…
• A question from conceptual physics (you
should totally be able to handle this one): A
horse is pulling a cart. In doing so, the cart
pulls on the horse with equal force. Why isn’t
this a futile exercise? Why is that the horse is
able to pull the cart?
….And then…
• Scott Keeler grows up to become an
astronaut. While working in space, he pushes
on a satellite (11,000kg) with a force of 36 N.
If his mass is 92 kg, what is the force on him
from the satellite? What are both object’s
acceleration?
• -36N, 0.0033 m/s2, -0.39 m/s2.
….And then…
• What is the equation for the law of universal
gravitation?
• What is the value of G?
• For two point masses of 20 and 25 kg
separated by 3 m, what is the force of gravity
they exert on each other?
….And then…
• The mass of the earth is 5.9742 × 1024 kg and
the mass of the sun is 1.99 X 10 30 kg. They
are separated by a distance of 146 X 109 m.
What is the magnitude of the gravitational
attraction on the earth by the sun?
• 3.72 X 1022 N
….And then…
• Saturn has an equatorial radius of 6 X 107 m
and a mass of 5.67 X 1026 kg. What is the
acceleration due to gravity at the equator of
Saturn?
• 10.5 m/s2
….And then…
• What is weight?
• What is the equation for weight on the surface
of earth?
• What is the difference between weight and
the force of gravity on an object?
• Suppose the force of gravity on an object is 20
N when it is sitting a distance X from the
center of a second object. If X is doubled, how
does the force of gravity change?
….And then…
• A 12 kg object sits at rest on a table. What is
its weight?
• What is the normal force on it from the table?
• If I push down on the object with an
additional 6 N force, what is the normal force
now from the table?
• If I pull up on the object with a 6 N force
instead, what is the normal force from the
table?
….And then…
• What is apparent weight?
• What is the difference between apparent
weight and actual weight?
• If a 300 N man is on an elevator that is
accelerating upwards at 2 m/s2, what is the
man’s apparent weight?
• What about if it is descending at 2 m/s2?
….And then…
• What is the difference between static and
kinetic friction?
• Write the equation for frictional force.
• If the normal force is 40 N and the coefficient
of friction is 0.3, what is the frictional force?
….And then…
• State the conditions for equilibrium.
• Travis Risinger is leaning at an angle of 450
against a wall. Name all the forces at work in
this system. What is the net force on Travis?
• Can you have equilibrium at constant velocity?
….And then…
• A system of masses and a pulley is show
below. If there is no friction, what is the
acceleration in the system?
• What is the coefficient of static friction
required to keep the system at rest?
m1 = 2 kg
m2 = 3 kg
….And then…
• An object is moved from sea level to the top
of Mount Everest. Which changes: mass,
weight, both, or neither?
• Object 1 weighs twice as much as object 2 at
the same spot on earth. Would the same be
true at the same place on Mars?
….And then…
• A box is stationary on an elevator floor.
Because of static friction, a force is required to
get the box moving horizontally. Rank the
force necessary for the situations when the
elevator is stationary, accelerating downwards
and accelerating upwards. Explain.
….And then…
• Two bottle rockets are launched, one pointed
straight up and one pointed horizontally.
Ignoring friction and air resistance, which
experiences the greater acceleration? Explain.
….And then…
• A rollercoaster is accelerated from rest to 45
m/s in 7sec. The total mass of the coaster plus
riders is 5.5 X 103 kg. What is the average net
force exerted on the coaster?