PHTY206 Lecture 8: Principles of management of overusechronic injuries

1.As a rocket rises its acceleration increases. Why does thishappen? (assume that the acceleration due to gravity and airresistance are nearly constant during the ascent)

2. If the head of the hammer is loose, and you wish tighten it bybaging it against the top of a work benchm why si it bettwee tohold it with the handle down ( as indicated in the diagram to theright) than to hold with the head down?

3. If a four-engine jet accelerate down a runway at 2.0m/s^2 andone of its engines suddenly fails, how much acceleration will theramaining three produce? ( asuume that all four engines areidentical.)

4. If an elephant was chasing you, its enourmous mass would be mostthreatning, but if made a quick turn, its mass would be to youradvantage. Why?

5. Many automobile passengers waiting at traffic lights havesuffered nech injuries when their cars were struck from behind.Explain why this happens, how can head rests reduce the severity ofthis type of injury?

6. Some people used to think that a spaceship could not maneuverover it left the earths's atmosphere because it would have no airto push against, obiviously, this thinking must be wrong sincerocket engines have been used to steer vehicles through space sincethe late 1950s. how does a rocket engine manage to apply a force toa spaceship in the vacuum of outer space?

7. If a bicycle and a truck have a head-on collision, which vehicleexperiences the greater force? which undergoes the greateraccleration?

8.two closed containers look the same, but one is tightly packedwith lead and the other loosely packed with feathers. how could youdetermine which was which if you and the containers were weightlessin outer space?

9. Two teams are involved in a tug-of-war. why is it wrong to saythat the team that pulls the hardest wins? what force realllydetermines who wins?

10. The photo on the website shows a physics teacher sandwichebetween two bed of nails. A second physics teacher is pulverizing acement block on top of the upper bed with a sledgehammer. If thecement block were replaced with a smaller brick, would thedemonstration be more or less safe?

Traumatic brain injury such as concussion results when the headundergoes a very large acceleration. Generally, an accelerationless than 800 m/s2 lasting for any length of time will not causeinjury, whereas an acceleration greater than 1000 m/s2 lasting forat least 1 ms will cause injury. Suppose a small child rolls off abed that is 0.38 m above the floor. If the floor is hardwood, thechild's head is brought to rest in approximately 1.9 mm. If thefloor is carpeted, this stopping distance is increased to about 1.0cm. Calculate the magnitude and duration of the deceleration inboth cases, to determine the risk of injury. Assume that the childremains horizontal during the fall to the floor. Note that a morecomplicated fall could result in a head velocity greater or lessthan the speed you calculate.

Hardwood floor magnitude	m/s2	duration	ms
Carpeted floor magnitude	Your response differs from the correct answer by more than 10%.Double check your calculations. m/s2	duration	Your response differs from the correct answer by more than 10%.Double check your calculations. ms

Traumatic brain injury such as concussion results when the headundergoes a very large acceleration. Generally, an accelerationless than 800 m/s2 lasting for any length of time will not causeinjury, whereas an acceleration greater than 1000 m/s2 lasting forat least 1 ms will cause injury. Suppose a small child rolls off abed that is 0.38 m above the floor. If the floor is hardwood, thechild's head is brought to rest in approximately 1.9 mm. If thefloor is carpeted, this stopping distance is increased to about 1.0cm. Calculate the magnitude and duration of the deceleration inboth cases, to determine the risk of injury. Assume that the childremains horizontal during the fall to the floor. Note that a morecomplicated fall could result in a head velocity greater or lessthan the speed you calculate.
Hardwood floor magnitude 1Your answer is correct. m/s2 duration2Your answer is correct. ms
Carpeted floor magnitude 3Your answer is incorrect.
Your response differs from the correct answer by more than 10%.Double check your calculations. m/s2 duration 4Your answer isincorrect.
Your response differs from the correct answer by more than 10%.Double check your calculations. ms