Physics 1029A/B Lecture Notes - Lecture 1: Gravitational Energy

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blackcrab361

12 Dec 2017

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If fnet = 0, then wtotal=zero, then the velocity is not changing(constant) If drop a ball, the only thing is doing work is the force of gravity, so the total work done would be equal to the work done by the gravity, which is fd=mgd, a negative component. Wtotal of a pendulum would sum up to zero. Types of energy: kinetic, potential, elastic, thermal energy. The bumpy incline would be faster than the straight incline. The energy lost would be different due to friction f= n straight: d= length of the track h=height=dsin .

Related Questions

1) An object is moving with constant velocity. Which of the following statements is true?
a) A constant force is being applied in the direction of motion.
b) A constant force is being applied in the direction opposite of motion.
c) There are no forces acting on the object.
d) The net force on the object is zero.
e) There is no frictional force acting on the object.

2) You apply the same force to two objects. Object 1 has mass M and object 2 has mass 5M. The acceleration is
a) ten times that of object 1 b) five times that of object 1
c) the same as that of object 1 d) 1/5 as that of object 1

3) An object of weight W is in free-fall close to the surface of Earth. What is the force that the object exerts on Earth?
a) a force greater than W b) a force less than W
c) a force equal to W d) no force at all

4) A parking crate slides down an inclined ramp at constant velocity. Thus we can deduce that _
a) a frictional force is acting on it
b) a net downward force is acting on it
c) a net upward force is acting on it
d) it is not acted on by appreciable normal force
e) it is not acted on by appreciable gravitational force

5) A person applies a constant force of 20N to a rock of mass 1000kg for a total of 20 seconds. What is the work done by this person if the person does not move at all by this applied force?
a) 1000J b) 2000J c) 20,000J d) 0J e) 400J

6) If the net work done on an object is positive, then the object's kinetic energy.
a) decreases b) remains the same c) increases d) is zero

7) You throw a ball straight up. Compare the sign of the work done by gravity while the ball goes up with the sign of the work done by gravity while it goes down.
a) Work is + on the way up and + on the way down
b) Work is + on the way up and - on the way down
c) Work is - on the way up and + on the way down
d) Work is - on the way up and - on the way down

lavenderbat941

1) An object is moving with constant velocity. Which of thefollowing statements is true?
a) A constant force is being applied in the direction ofmotion.
b) A constant force is being applied in the direction opposite ofmotion.
c) There are no forces acting on the object.
d) The net force on the object is zero.
e) There is no frictional force acting on the object.

2) You apply the same force to two objects. Object 1 has mass M andobject 2 has mass 5M.
a) ten times that of object 1 b) five times that of object 1
c) the same as that of object 1 d) 1/5 as that of object 1

3) An object of weight W is in free-fall close to the surface ofEarth. What is the force that the object exerts on Earth?
a) a force greater than W b) a force less than W
c) a force equal to W d) no force at all

4) A parking crate slides down an inclined ramp at constantvelocity. Thus we can deduce that _
a) a frictional force is acting on it
b) a net downward force is acting on it
c) a net upward force is acting on it
d) it is not acted on by appreciable normal force
e) it is not acted on by appreciable gravitational force

5) A person applies a constant force of 20N to a rock of mass1000kg for a total of 20 seconds. What is the work done by thisperson if the person does not move at all by this appliedforce?
a) 1000J b) 2000J c) 20,000J d) 0J e) 400J

6) If the net work done on an object is positive, then theobject's kinetic energy.
a) decreases b) remains the same c) increases d) is zero

7) You throw a ball straight up. Compare the sign of the workdone by gravity while the ball goes up with the sign of the workdone by gravity while it goes down.
a) Work is + on the way up and + on the way down
b) Work is + on the way up and - on the way down
c) Work is - on the way up and + on the way down
d) Work is - on the way up and - on the way down

Some Problems on Work
1. Joe is pulling a box of mass m = 10 kg up an inclined surface (?= 30degrees) using
a rope. The coefficient of kinetic friction between the surface andthe box is
Âµk = 0.5. It takes 10 seconds for Joe to bring up a box at aconstant velocity
V = 0.8m=s.
(a) What is the tension of the rope?
(b) What is the work done by the tension?
(c) What is the work done by the normal force?
(d) What is the work done by gravity?
(e) What is the total work done on the box?
(f) What is the power output necessary to Joe to bring up thebox?
maximal compression of the spring?
2. A block (m=50 kg) slides down a 3 m long inclined surface (? =30). The
coefficient of kinetic friction between the block and the surfaceis Âµk = 0.3.
Calculate the nal velocity of the block using the work-energytheorem.
3. A pendulum of length l and mass m is released from rest at anangle ? from
the equilibrium position.
(a) Neglect air friction. Calculate the velocity of the pendulumwhen the angle
is zero. Express your result in terms of ?, l, and m.
(b) Suppose ? = 60 degrees and l = 1 m. Suppose that the velocityof the pendulum
when the angle is zero is 1 m/s. Calculate the work done by the airfriction.
4. A point particle of mass m = 20 g is moving on a
at
surface when it reaches a slope which brigs it up by h = 08 m. Thespeed of
the particle in position A is v = 5 m/s.
(a) Suppose that there is no friction. What is the velocity of theparticle when
it reaches position B?
(b) Suppose that there is friction, and that the velocity of theparticle in B is
0. What is the work done by the friction from A to B?
5. A ball is shoot vertically with initial speed v, from a
table of height h.
(a) Calculate the maximal height ymax that the ball can reach (b)Calculate the velocity of the ball just before it hits thefloor.

Physics 1029A/B Lecture Notes - Lecture 1: Gravitational Energy

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