Question

1. An engineer designing a roadside barrier seeks to reduce the force experienced by the occupants of a vehicle hitting the barrier. She can do nothing to change the velocity at impact or the mass of the occupants or the characteristics of a vehicle hitting the barrier. The only thing she can change is the depth of the barrier to increase the time of deceleration. This is because _________ remains constant during the crash.

a.Acceleration

b.displacement

c. Force

d. Impulse

2. The conservation of momentum requires.

a. An open system that interacts with its environment and its frictionless

b.A closed system that is isolated from the environment and frictionless

c. Kinetic energy that is greater than potential energy

d. potential energy

3. A 113 kg football coach is shouting encouragement at his players as they push against a three- position blocking sled which the coach is standing on. The three players shove the sled two meters. One player has a mass of 95 kg (#95), another 82 kg (#82) and a third 73 kg (#73). Which person is doing the least work and why?

a. #95 because he has less velocity

b. #82 because he has less weight

c.Coach because his weight acts perpendicular to the momvement of the sled

d. #73vbecause the other players are doing the work

4. A 1495 kg model of car is being used for crash tests into various barriers at 22.5 . When the first car is smashed into an immovable wall, it comes to a halt in 0.300 seconds. When the second car is smashed into a barrier of sand-filled barrels it comes to a halt in 0.85 seconds. What is the impact force on the second car?

5. On 25 July 1956, the 2.63x107 kg Italian cruise ship Andrea Doria steaming at 40.4 was rammed in fog by the 1.1x107 kg Swedish vessel Stockholm moving at 33.0 . Assume the Andrea Doria was moving south at the moment of impact, and the Stockholm was moving east, and that the two ships remained locked together after the collision. Ignore the drag of the water. Find the magnitude and direction of the velocity of the locked ships after the collision?

6. Worried about an attack by a rogue state, the U.S. Air Force launches a Project Thor satellite into low earth orbit. From an altitude of 250 km it drops a 110 kg Mjolnir projectile. What is the projectile’s velocity when it hits the ground in Area 52 in southwest Nevada? Ignore air resistance.

Answer 1

1) This is because the impulse remains constant during the crash. Impluse is the produce of the force and time of deceleration. By increasing time we can reduce the force. d is correct.

2) The conservation of momentum requires, net force on the system = 0 which means it requires a closed system that is isolated from the environment and frictionless. b is correct.

3) The coach is not doing any work at all. His weight and normal force on him act perpendicular to the movement of the sled so the work done by him = 0. c is correct.

answered by: anonymous