Physics 197 Lecture Notes - Lecture 1: Free Fall, Earth Radius, Friction

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27 Sep 2018

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Work-kinetic energy theorem: the work done by force f as it acts on an object that moves positions r1 and r2 is equal to the (cid:272)ha(cid:374)ge i(cid:374) the o(cid:271)je(cid:272)t"s ki(cid:374)eti(cid:272) e(cid:374)ergy (cid:894)(cid:373)ai(cid:374) (cid:272)o(cid:374)(cid:272)ept(cid:895, w=(delta)k. K increases. (force in similar directions) less than 90 degree angle: no energy is transferred. After the force is removed, the kinetic energy of the light plastic cart is ____b____ that of the heavy steel cart: greater than, equal to, less than, ca(cid:374)"t say, it depe(cid:374)ds ho(cid:449) (cid:271)ig the for(cid:272)e is. In which case does the object have the highest speed at the bottom: free fall, incline, string, all the same. All started the same, all will end the same. Only force acting is the force of gravity. The incline does(cid:374)"t do a(cid:374)y (cid:449)ork o(cid:374) the o(cid:271)je(cid:272)t; all forces are done by gravity. Take the component of the force along the displacement.

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

Part A.

Blocks A, B, and C are pushed across a frictionless table by a hand that exerts a constant horizontal force. Block A has mass 2M block B has mass 3M and block C has mass M.

a) Draw separate free-body diagrams for each of the three blocks. Clearly label the forces. in the spaces below, draw vectors to represent the net force on each block.
b) Draw the vectors with correct relative magnitudes.

Part B.

Blocks A and B are at rest on a level, frictionless surface. Block B is attached to an ideal massless spring of constant k, which is initially at its equilibrium length. Block B has greater mass than block A (m_B > m_A).

During the interval from t₁ to t₂ a hand pushes block A to the left with a constant force of magnitude F₀, compressing the spring a distance as shown. At time t₂, both blocks again have a speed of zero.

Consider system A consisting of block A and system BS consisting of block B and the spring.

c) During the interval from t₁ to t₂, is the absolute value of the net work done on system BS by external forces, greater than, less than, or equal to that done on system A by external forces?

At some later time, the hand is holding the blocks at rest with the spring compressed a distance d₀. At time t₃ the hand releases the blocks. At time t₄, the spring returns to its equilibrium length and both blocks have speed v_f, as shown.

Consider the interval from t₃ to t₄:

d) Is the change in kinetic energy of system BS greater than, less than, or equal to that of system A?
e) Is the change in total energy of system BS positive, negative, or zero?

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Physics 197 Lecture Notes - Lecture 1: Free Fall, Earth Radius, Friction

Physics 197 Full Course Notes

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Part A.

Part B.