Physics 2414

Midterm #3 – 2004

Version A

Multiple Choice (7 pts each)

  1. Two pucks are pushed along an air hockey board Finish (which is frictionless). Puck A has three times the mass of puck B. Each puck is pushed for the same distance from the start line to the finish line with the same amount of force. Consider the motion of the pucks at the finish line. Start Which of the following statements is true? A 3m m B

A)The momentum and kinetic energy of the pucks are equal F F

B)The momentum of the pucks is equal but the kinetic energy of the pucks is not equal

C)The momentum of the pucks is not equal but the kinetic energy of the pucks is equal

D)Neither the momentum not the kinetic energy of the pucks are equal

E)The time it takes to push the pucks from the start to the finish line is the same for A and B

  1. A car with a mass of 1000 kg crashes into a parked pickup truck with a mass of 1500 kg. The two vehicles stick together and slide along the road before they stop. Which vehicle had the greatest change in momentum during the collision and which vehicle had the greatest momentum immediately after the collision?

Greatest Change in magnitude of momentum Greatest momentum immediately after collision

A) Car Car

B) Car Truck

C) Car Same

D) Same Same

E) Same Truck

3. A car of mass m, traveling with a velocity v, strikes a parked truck with a mass of 2m. The bumpers lock together in this completely inelastic collision. What fraction of the initial kinetic energy is lost in this situation?

A)None

B) ¼

C)½

D)2/3

E)1/3

  1. The figure below depicts the paths of two colliding steel balls, X and Y.

Y

X

Which set of arrows best represents the direction of the change in momentum of each ball?

X

A) X Y B) X Y C) D) X Y E) X Y

Y

  1. You are in a very light stationary sealed train car of length 10 m on a frictionless track. Inside there is a large number of very heavy cannonballs stacked on one side and a cannon. By shooting the cannonballs inside the train car, what is the maximum distance you can move the train car? (assume that the mass of the train and cannon are very small compared to the mass of all the cannonballs. The cannonballs can never leave the sealed train car)

A)10 m

B) 5 m

C)You can move it any distance you want, it depends on the number of cannonballs and how hard you shoot them

D)20 m

E) You cannot move the train car no matter what you do

Show all of your work on the answer sheet. No credit will be given if work is not shown

  1. (33 pts ) A plane of mass 10000 kg is flying at 100 m/s at an angle of 30 degrees below the horizontal. When it is 1000 m above the ground, it explodes into 2 pieces. One large piece of mass 9000 kg falls straight down. The other small piece goes off at 45 degrees above the horizontal.

A)What are the velocities of the two pieces immediately after the explosion?

B) The small piece is very small and experiences no wind resistance. What is the kinetic energy of the small piece when it hits the ground?

C)The large piece experiences a frictional force due to the wind of 900 N on the way down. What is the kinetic energy of the large piece when it hits the ground?

  1. (32 pts) A 1400 kg block of granite is pulled up a plane at a constant speed of 1.0 m/s by a steam winch. The coefficient of kinetic friction between the block and plane is 0.40.

A)How much work is done by each of the forces that act on the block as it moves 9.0 m along the incline.

B)How much power must be supplied by the winch

Just when the block of granite reaches the top, the rope breaks and the block slides down the plane. At the bottom of the plane is a spring with spring constant k=1000 N/M.

C)How far does the spring compress due to the block?