1 meter

400 m/sec

A marksman holds his rifle perfectly horizontal and directs his fire straight over flat and level

terrain. The rifle bullet leaves its barrel traveling at 400 m/sec.

Once the bullet leaves the barrel it experiences

A. a forward force equal to its momentum.B. a forward force equal to its weight.C. only the downward force of its weight.D. a forward force that is equal to its inertia.

1 meter

400 m/sec

A marksman holds his rifle perfectly horizontal and directs his fire straight over flat and level

terrain. The rifle bullet leaves its barrel traveling at 400 m/sec.

How long is this bullet in the air?

A.

C.

E. seconds8.408.9

400 seconds4.208.9

200

B.

D.

F.

seconds102.08.9

1

seconds45.08.9

2

seconds204.08.9

2

seconds042.02

8.9

2

1 meter

400 m/sec

A marksman holds his rifle perfectly horizontal and directs his fire straight over flat and level

terrain. The rifle bullet leaves its barrel traveling at 400 m/sec.

The bullet is in the air for 0.45 seconds.How far down range does it strike ground?

A.B.C.D.

E.

meters secm/sec 90)45.0)(200(

meters secm/sec 180)45.0)(400(

meter secm/sec 2 99.0)45.0)(8.9( 2

21

meters

secm/sec secsecm 2

181

)45.0)(8.9()45.0)(/400( 2

21

meters

secm/sec secsecm 2

179

)45.0)(8.9()45.0)(/400( 2

21

1 meter

400 m/sec

A marksman holds his rifle perfectly horizontal and directs his fire straight over flat and level

terrain. The rifle bullet leaves its barrel traveling at 400 m/sec.

The bullet is in the air for 0.45 seconds.It strikes the ground 180 meters down range.

Another rifle with center-fire cartridges shoots bullets with twice the speed: 800 m/sec.They land down range after traveling

A. the same the distance: 180 meters.B. the times as far: 254 meters.C. twice the distance: 360 meters.D. four times the distance: 720 meters.

2

Momentum = mass velocity

Kinetic energy = mass (velocity)212

F t = (mv)Impulse:

change in momentum

stoppingtime

F d = ( mv2)Work:

change in kinetic energy

stoppingdistance

12

You temporarily lose control of your vehicleand crash headlong into a solid brick wall.The 600 kg car was traveling 24 m/sec, the front end has been pushed 1 full meter back into the frame. The wall didn’t move at all.

What was the car’s average speedwhile moving in contact with the wall?

A. zero.

B. 2 m/sec.

C. 6 m/sec.

D. 12 m/sec.

E. 18 m/sec.

You temporarily lose control of your vehicleand crash headlong into a solid brick wall.The 600 kg car was traveling 24 m/sec, the front end has been pushed 1 full meter back into the frame. The wall didn’t move at all.

Before impact the car had how much momentum?

A.

B.

C.

D.

secmkg m/sec kg /200,7)24)(600(21

m/seckg m/sec kg 400,14)24)(600(22

21 /800,172)24)(600( secmkg m/sec kg 2

22 /600,345)24)(600( secmkg m/sec kg 2

You temporarily lose control of your vehicleand crash headlong into a solid brick wall.The 600 kg car was traveling 24 m/sec, the front end has been pushed 1 full meter back into the frame. The wall didn’t move at all.

Before impact the car had how much kinetic energy?

A.

B.

C.

D.

secmkg m/sec kg /200,7)24)(600(21

m/seckg m/sec kg 400,14)24)(600(22

21 /800,172)24)(600( secmkg m/sec kg 2

22 /600,345)24)(600( secmkg m/sec kg 2

You temporarily lose control of your vehicleand crash headlong into a solid brick wall.The 600 kg car was traveling 24 m/sec, the front end has been pushed 1 full meter back into the frame. The wall didn’t move at all.

Before impact the car had 172,800 kg·m2/sec2 of kinetic energy 14,400 kg·m/sec of momentum.

What was the force of impact on the car?A. 600 NewtonsB. 5,880 NewtonsC. 14,400 NewtonsD. 28,800 NewtonsE. 172,800 NewtonsF. 345,600 Newtons

You temporarily lose control of your vehicleand crash headlong into a solid brick wall.The 600 kg car was traveling 24 m/sec, the front end has been pushed 1 full meter back into the frame. The wall didn’t move at all.

Before impact the car had 172,800 kg·m2/sec2 of kinetic energy 14,400 kg·m/sec of momentum.

How much time did it take the car to stop?A. 1/24 sec = 0.0417 secB. 1/12 sec = 0.0833 secC. 1/6 sec = 0.1667 secD. 1/4 sec = 0.2500 secE. 1/2 sec = 0.5000 sec

You temporarily lose control of your vehicleand crash headlong into a solid brick wall.The 600 kg car was traveling 24 m/sec, the front end has been pushed 1 full meter back into the frame. The wall didn’t move at all.

Before impact the car had 172,800 kg·m2/sec2 of kinetic energy 14,400 kg·m/sec of momentum.

What impulse did the car deliver to the wall?

A. zero (no impulse). B. 14,400 kg·m/secC. 28,800 kg·m/secD. 86,400 kg·m2/sec2

E. 172,800 kg·m2/sec2

F. 172,800 Newtons

You temporarily lose control of your vehicleand crash headlong into a solid brick wall.The 600 kg car was traveling 24 m/sec, the front end has been pushed 1 full meter back into the frame. The wall didn’t move at all.

Before impact the car had 172,800 kg·m2/sec2 of kinetic energy 14,400 kg·m/sec of momentum.

How much work did the car do on the wall?

A. zero (no work). B. 14,400 kg·m/secC. 28,800 kg·m/secD. 86,400 kg·m2/sec2

E. 172,800 kg·m2/sec2

F. 172,800 Newtons

You temporarily lose control of your vehicleand crash headlong into a solid brick wall.The 600 kg car was traveling 24 m/sec, the front end has been pushed 1 full meter back into the frame. The wall didn’t move at all.

Before impact the car had 172,800 kg·m2/sec2 of kinetic energy 14,400 kg·m/sec of momentum.

Where did the kinetic energy of the car go?

A. It is now stored in the bent metal parts of the car.

B. It did work by slightly raising the center of mass of the car.

C. It generated thermal energy within the car and wall.

D. it was all transferred by the impulse to the wall.

A. you would transfer more momentum to the steering wheel than you do to the airbag.B. you would transfer more energy to the steering wheel than you do to the airbag. C. you transfer the same momentum in either case, but it takes longer with the airbag. D. you transfer the same energy in either case, but the transfer takes longer with the airbag.

Having your head stopped by an airbag is safer than by the steering column because

A 10-kg sign hangsfrom two chains so

that each chain shares the load equally.

The weight borne by the individual eyelet fastener holding each chain at the top is

A. 5 kilogramsB. 10 kilogramsC. (5 kg)(9.8 m/sec2) = 49 NewtonsD. (10 kg)(9.8 m/sec2) = 98 NewtonsE. between 49 – 98 Newtons.

A simple pulley just redirects the lifting force.

The hook in the ceiling holding the block and tackle in place, provides how much totalforce in support as this weight is lifted?

???

F=?

The force F an operator must apply by hand to hold this 200 lb weight in place is?

A. 50 lbs B. 100 lbs. C. 200 lbs.D. 250 lbs E. 300 lbs. F. 400 lbs.

The force F an operator must apply by hand to hold this 200 lb weight in place is?

The work by the operator holding this 200-lb weightin place is

F

A. positive. B. zero.C. negative.

Raising this weight6 feet with this blockand tackle involves

A. half the work raising it 6 feet by hand without the pulley.B. the same amount of work as raising it 6 feet by hand without the pulley.C. twice as much work as raising it 6 feet by hand without the pulley.

The work by the operator holding this 200-lb weightin place is

A. positive. B. zero.C. negative.

This child lifts his basketfullof blocks by

pulling with a force equal to

A. ¼ its weight.B. ½ its weight.C. its weight.D. 2 its weight.E. 4 its weight.

To raise it adistance h hemust draw in what length of rope?

A. ¼hB. ½hC. hD. 2hE. 4h

A crate is wheeled up a ramp into the back of a delivery truck, its wheels providing a

smooth, almost friction-free ride.

5 feet

12 feet

13 feet

The workman must push forward with a force equal to

A. (5/12) the weight of the cart.B. (5/13) the weight of the cart.C. (12/13) weight of the cart.D. the full weight of the cart.E. (13/12) the weight of the cart.F. (13/5) the weight of the cart.

Several ramps of different length are available.

B. 13 feet

When using the 26-foot ramp, the workman must push forward with a force equal to

A. twice the force needed on ramp B.B. the same force needed on ramp B.C. half the force needed on ramp B.D. the full weight of the cart.

C. 26 feetA. 8 feet

5 fe

et

A. Using ramp A requires the most work.B. Using ramp B requires the most work.C. Using ramp C requires the most work.D. The same amount of work is done

using any of these ramps.

When an object is pushed or pulled by a force that is completely balanced

A. no work is possible.B. the kinetic energy of that object decreases.C. potential or thermal energy is produced as a consequence.

In each of these examples the force being exerted by each worker is exactly balanced by another force!

by elastic forces

by weight

by friction

Lecture 11: 20 Questions1. C only weight 2. D 0.45 sec3. B 180 meters4. C twice5. D ½(24 m/sec) = 12 m/sec6. B 14,400 kg·m/sec7. C 172,800 kg·m2/sec2 8. E 172,800 N9. B 1/12 sec10. B 14,400 kg·m/sec11. A zero12. C thermal energy13. C takes longer14. C 49 N15. B 100 lbs.16. E 300 lbs.17. B zero18. B the same19. A ¼ 20. E 4h21. B (5/13)22. D the same23. C half24. C potential and thermal energy

2

21 atd adt /2

vtd It has 0.45 sec to move forward.It also has the same 0.45 sec to move forward.

22 /800,172 smkgFd and d= 1 meter.

vavg = 12 m/sec and d = 1 meter.

impulse, Ft, = change in momentum.“The wall doesn’t move at all.”

Same total Ft, but longer t.

Mass is not weight. W = mg.

There are 3 100-lb forces all pulling down.“to hold in place” means d=0.

Total work still same: ¼F(4h)=Fh