PHYS 1420 Lecture Notes - Lecture 15: Dot Product, Net Force, International System Of Units

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maroongrasshopper46

21 Oct 2017

School

York University

Department

Physics and Astronomy

Course

PHYS 1420

Professor

Matthew George

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Document Summary

Joule (j: can be positive or negative. If the force and displacement are in the same direction, work is positive. If an applied force and displacement are perpendicular, then no work is done: more than one force can do work on an object. Is there work done by your arms when lifting up a textbook: yes. Is there work done by your arms when carrying a textbook: no. Is there work done by your arms when outing down a textbook: yes. Dot product: also called scalar product operates on two vectors and returns a scalar, a*bcos , : the angle between a and b , and is always positive. If =180 then a *b = -ab: dot product is commutative: a *b = b *a , dot product is distributive: a *(b +c )= a *b = a *c . If we do work on an object, we are applying a force in the direction of motion.

Related Questions

1. Can work be done on a system if there is no motion?

A) Yes, if an outside force is provided B) Yes, since motion is only relative C) No, since a system which is not moving has no energy D) No, because of the way work is defined

2. The quantity 1/2 mv 2 is

A) the power supplied to the object by the force B) the work done on the object by the force C) the kinetic energy of the object. D) the potential energy of the object.

3. If you push twice as hard against a stationary brick wall, the amount of work you do

A) doubles. B) is cut in half C) remains constant but non-zero D) remains constant at zero

4. If the net work done on an object is positive, then the object's kinetic energy

A) increases. B) decreases C) remains the same D) is zero

5 A force of 20 N moves an object in the direction of the force. The work done when the object moves from 2.0 to 4.0 m is o A) 20 J OB) 40 J oC) 60 J D) 80 J

whitemosquito79

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

PHYS 1420 Lecture Notes - Lecture 15: Dot Product, Net Force, International System Of Units

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