Energy, Work and Momentum Test

Name______

Class/Period______

Physics

Wednesday, January 14th

Format

1) 30 Multiple Choice Questions (1 pt. each)

2) 6 Short Answer (5 points each)

Study Material – Multiple Choice

1) Class Notes

2) Quizzes

3) Lab Experiences

4) Online Activities

5) Review Packet

Study Material – Short Answer

1) Energy Definitions

2) Energy Calculations

3) Work Calculations

4) Simple Machines Explanations

5) Mechanical Advantage Definition

6) Momentum Problems

5) Impulse Problems

6) Conservation of Momentum Problems

Notes and Formulas

Questions

1) Define potential energy, units for it, and the formula to calculate it.

2) Define kinetic energy, units for it, and the formula to calculate it.

3) Define work, units for it, and the formula to calculate it.

4) If a 85 kg person climbs to the top of a 22 m house, how much kinetic energy will he have?

5) If the same person jumps off the roof onto a trampoline which is 2 m off the ground, how much kinetic energy will he have when first hitting the trampoline?

6) If a biker with a total mass of 100 kg is cycling at 16 m/s, what is her kinetic energy?

7) If a 772 kg car is moving at 55 km/hr, what is its kinetic energy?

8) What is the law of conservation of energy?

9) Define energy.

10) List and describe the 8 types of energy.

11) Name, describe, and give an example of all six simple machines.

12) What does a simple machine do?

13) What doesn’t a simple machine do?

14) What is mechanical advantage?

15) What is the trade-off in using a simple machine to make work “easier?”

16) Compare the amount of work done with a simple machine and the potential energy of the object moved.

17) If a ramp is .6m tall and 16 m long, calculate the work and PE if a 4 kg car needs 2 N to pull it up the ramp.

18) A 55 kg boy on a skateboard has a momentum of 231 kg m/s. What is his velocity?

19) If a go kart has a mass of 200 kg and a velocity of 8.5 m/s, what is its momentum?

20) Auto companies frequently test the safety of automobiles by putting them through crash tests to observe the integrity of the passenger compartment. If a 1000 kg car is sent into a cement wall with a speed of 14 m/s and the impact brings it to a stop in 8.0 x 10-2 seconds, with what average force is it brought to rest?

21) If the girl in Wayne’s World riding a bike is moving at 2 m/s and the total mass of her and the bike is 85 kg, how much time does it take to stop if the force exerted on her when she hits the car is 200 N?

22) Maurice is waiting to make a billiard shot. Each of the pool balls has a mass of 80 grams and the cue ball comes to a complete stop upon making contact with the 8 ball. Suppose Maurice hits the cue ball by exerting a force of 180 N for 5.00 x 10-3 seconds. Calculate the resulting velocity of the 8 ball.

23) Tubby and his twin brother Chubby have a combined mass of 200 kg and are zooming along in a 100 kg bumper car at 10 m/s. They bump Melinda’s car, which is sitting still. Melinda has a mass of 25 kg. After the elastic collision, the twins continue ahead with a speed of 4.12 m/s. How fast is Melinda’s car bumped across the floor?

24) Anthony and Sissy are participating in a rollerskating dance. While 75 kg Anthony rollerskates backwards at 3.0 m/s, 60 kg Sissy jumps into his arms with a velocity of 5 m/s in the same direction. How fast does the pair roll backwards together?

25) A group of students from the soccer team decide to go bowling, but decide to make their own game using a soccer ball. They kick the ball down the lane to try to knock over pins. Once student knocked over all but one pin and is kicking to get it now. He kicks the 1 kg ball with a velocity of 13 m/s. It hits the 3.5 kg pin and bounces back towards the kicker with a velocity of 2 m/s. What is the velocity of the pin after being hit with the soccer ball?

Answer Key

1) Define potential energy, units for it, and the formula to calculate it.

Potential energy is stored energy, measured in Joules (J), and is calculated as PE = mgh.

2) Define kinetic energy, units for it, and the formula to calculate it.

Kinetic energy is energy in motion, measured in joules (J), and calculated as KE = ½mv2

3) Define work, units for it, and the formula to calculate it.

Work is force applied to move something, measured in J, and calculated as Work =fd

If an object does not move, no work was done.

4) If a 85 kg person climbs to the top of a 22 m house, how much kinetic energy will he have?

Don’t know parts to calculate KE, but not moving, so KE = 0

PE = mgh

PE = (85 kg)(10 m/s2)(22m)

PE = 18700 J

5) If the same person jumps off the roof onto a trampoline which is 2 m off the ground, how much kinetic energy will he have when first hitting the trampoline?

Use the fact that the total energy of the person (18700 J) never changes (the law of conservation of energy tells us this). The energy only changes form, so –

PE = (85 kg)(10 m/s2)(2m)

PE = 1700 J

KE = Total Energy – PE

KE = 18700 J – 1700 J

KE = 17000 J

6) If a biker with a total mass of 100 kg is cycling at 16 m/s, what is her kinetic energy?

KE = ½mv2

KE = ½(100 kg)(16m/s)2

KE = 12800 J

7) If a 772 kg car is moving at 55 km/hr, what is its kinetic energy?

First, v must be in m/s, so

55 km * 1000 = 55000 m

1 hr * 60 = 60 min * 60 = 3600 sec

v = 55000 m/3600 s

KE = ½(772 kg)(55000m/3600sec)2

KE = 90096 J

8) What is the law of conservation of energy?

Energy can not be created or destroyed

9) Define energy.

Energy is the ability to do work

10) List and describe the 8 types of energy.

Mechanical- –Motion of objects

Heat – how much the atoms vibrate

Sound – vibration of molecules in a pattern created by a source

Electromechanical – light & radio waves

Electrical – moving electrons

Magnetic – attraction and repulsion of north & south poles

Chemical – based on chemical reactions

Nuclear – fusing atoms together or splitting (fission) atoms apart

11) Name, describe, and give an example of all six simple machines.

Incline plane, a ramp that gives a slope to push/pull something up, a driveway up a hill, a handicapped access ramp

Wedge, one or two incline planes that push into something causing parts to be pushed apart, a knife or axe

Screw, an incline plane wrapped around a cylinder, a spiral staircase

Lever, a beam with a fulcrum (pivot point) that moves

1st class, fulcrum in the middle – seesaw

2nd class, fulcrum at the end, load in the middle – wheelbarrow

3rd class, fulcrum at the end, load at the other end – tennis racket, fishing pole

Pulley, one or more pulleys with rope running through, a block and tackle from a sailing boat

Wheel & Axle, a wheel & axle attached, one rotates the other

Wheel & axle of a car – spin axle causes wheel to rotate

Doorknob – turn larger “wheel” causes smaller axle to rotate

12) What does a simple machine do?

A simple machine will change the magnitude or direction of a force

It appears to make work easier

13) What doesn’t a simple machine do?

It does not make for less work

14) What is mechanical advantage?

How much the force is multiplied

The block and tackle used to pull students into the air had a mechanical advantage of 4. I pulled with 50 lbs and could lift 200 lbs

15) What is the trade-off in using a simple machine to make work “easier?”

If we pull with less force, we must pull for a longer distance

16) Compare the amount of work done with a simple machine and the potential energy of the object moved.

In a perfect world without friction, the amount of work would be the same as the potential energy gained by the object.

It the real world, friction causes us to do more work using a simple machine.

17) If a ramp is .6m tall and 16 m long, calculate the work and PE if a 4 kg car needs 2 N to pull it up the ramp.

w = fdPE = mgh

w = (2N)(16m)PE = (4kg)(9.8 m/s2)(.6m)

w = 32 JPE = 23.52 J

Work is more than PE because of friction on the ramp while sliding the car up it.

18) A 55 kg boy on a skateboard has a momentum of 231 kg m/s. What is his velocity?

M=55 kgp=mv231 kg m/s = (55 kg)V

V=?231 kg m/s /55kg = (55 kg)V/55kg

P=231 kg m/sV=4.2 m/s

19) If a go kart has a mass of 200 kg and a velocity of 8.5 m/s, what is its momentum?

M=200 kgp=mvp = (200 kg)(8.5 m/s)

V=8.5 m/sp = 1700 kg m/s

P=?

M = 1000 kgFΔT=MΔVF(8.0X10-2 s) = (1000 kg)(-14 m/s)

ΔV - -14 m/sF(8.0X10-2 s) = -14000 kg m/s

T= 8.0 x 10-2 s

F=(-14000 kgm/s)/8.0X10-2 s

F=-175,000 N

M = 85 kgFΔT=MΔV(-200N)T = (85 kg)(-2 m/s)

ΔV -2 m/s(-200N)T = (-175 kg m/s)

T= ?T = (-175 kg m/s)/(200N)

F= -200NT= .85 s

FΔT=MΔV

V=(FΔT)/M

(180 N)(5.0X10-3 sec)/.08 kg

V=11.3 m/s

M1 = 300 kgM1V1i + M2V2i = M1V1f + M2V2f

M2 = 125 kg(300)(10) + (125)(0) = (300)(4.12) + (125)Vf

V1i = 10 m/s 3000 = 1236 + (125)Vf

V2i = 0 m/s 3000 - 1236= 1236 + (125)Vf- 1236

V1f = 4.12 m/s Vf = (1764)/125

V2f = ? m/s V2f = 14.1 m/s

M1 = 75 kg M1V1i + M2V2i = (M1 + M2)Vf

M2 = 60 kg (75)(3) + (60)(5) = (75+60)Vf

V1i = 3 m/s 225 + 300 = (135)Vf

V2i = 5 m/s Vf = (525)/(135)

Vf = ? m/sVf = 3.9 m/s

M1 = 1 kgM1V1i + M2V2i = M1V1f + M2V2f

M2 = 3.5 kg(1 kg)(13 m/s) + (3.5 kg)(0 m/s) = (1 kg)(-2 m/s) + (3.5 kg)V2f

V1i = 13 m/s 13 kg m/s = -2 kg m/s + (3.5 kg)V2f

V2i = 0 m/s 13 kg m/s + 2 kg m/s= -2 kg m/s + (3.5 kg)V2f + 2 kg m/s

V1f = -2 m/s (15 kg m/s)/3.5 kg

V2f = ? m/s V2f = 4.29 m/s