Test – Chapters 5-6: Work, Power, Momentum, Impulse

Do NOT write on this test. Write all answers on your own paper – SHOW ALL YOUR WORK!

Good luck!

  1. A football is kicked off the ground a distance of 50 yards downfield. Neglecting air resistance, which of thefollowing statements would be INCORRECT when the football reaches the highest point?

(A)all of the balls original kinetic energy has been changed into potential energy

(B)the balls horizontal velocity is the same as when it left the kickers foot

(C)the ball will have been in the air one-half of its total flight time

(D)the ball has an acceleration of g

(E)the vertical component of the velocity is equal to zero

  1. A rock is dropped from the top of a tall tower. Half a second later another rock, twice as massive as the first, isdropped. Ignoring air resistance,

(A)the distance between the rocks increases while both are falling.

(B)the acceleration is greater for the more massive rock.

(C)the speed of both rocks is constant while they fall.

(D)they strike the ground more than half a second apart.

(E)they strike the ground with the same kinetic energy.

  1. Which of the following is true for a system consisting of a mass oscillating on the end of an ideal spring?

(A)The kinetic and potential energies are equal to each other at all times.

(B) The kinetic and potential energies are both constant.

(C)The maximum potential energy is achieved when the mass passes through its equilibrium position.

(D)The maximum kinetic energy and maximum potential energy are equal, but occur at different times.

(E)The maximum kinetic energy occurs at maximum displacement of the mass from its equilibrium position

Questions 4-5

A ball swings freely back and forth in an arc from point I topoint IV, as shown. Point II is the lowest point in the path,III is located 0.5 meter above II, and IV is I meter above II. Air resistance is negligible.

  1. If the potential energy is zero at point II, where will thekinetic and potential energies of the ball be equal?

(A) At point II (B) At some point between II and III

(C) At point III (D) At some point between III and IV

(E) At point IV

  1. The speed of the ball at point II is most nearly

(A) 3.0 m/s (B) 4.5 m/s (C) 9.8 m/s (D) 14 m/s (E) 20 m/s

  1. An object of mass m is lifted at constant velocity a vertical distance H in time T. The power supplied by thelifting force is

(A) mgHT (B) mgH/T (C) mg/HT (D) mgT/H (E) zero

  1. A force F is exerted by a broom handle on the head of the broom, which has amass m. The handle is at an angle θ to the horizontal, as shown. The workdone by the force on the head of the broom as it moves a distance d across ahorizontal floor is

(A)Fd sin θ (B) Fdcosθ(C) Fm cosθ(D) Fm tanθ(E) Fmdsinθ

  1. A descending elevator of mass 1,000 kg is uniformly decelerated to rest over a distance of 8m by a cable in which the tension is 11,000 N. Thespeed vi of the elevator at the beginning of the 8 m descent is mostnearly

(A) 4 m/s (B) 10 m/s (C) 13 m/s

(D) 16 m/s (E) 21 m/s

  1. A deliveryman moves 10 cartons from thesidewalk, along a 10-meter ramp to aloading dock, which is 1.5 meters abovethe sidewalk. If each carton has a mass of25 kg, what is the total work done by thedeliveryman on the cartons to move themto the loading dock?

(A)2500 J (B) 3750 J (C) 10000 J (D) 25000 J (E) 37500 J

  1. Two objects, P and Q, have the same momentum. Q can have more kinetic energy than P if it has:

(A) More mass than P (B) The same mass as P (C) More speed thanP

(D) The same speed at P (E) Q can not have more kinetic energy than P

  1. A spring is compressed between two objects with unequal masses, m and M, and held together. The objects areinitially at rest on a horizontal frictionless surface. When released, which of the following is true?

(A)Kinetic energy is the same as before begin released.

(B)The total final kinetic energy is zero.

(C)The two objects have equal kinetic energy.

(D)The speed of one object is equal to the speed of the other.

(E)The total final momentum of the two objects is zero.

  1. A 5000 kg freight car moving at 4 km/hr collides and couples with an 8000 kg freight car which is initially atrest. The approximate common final speed of these two cars is

(A)1 km/h (B) 1.3 km/h (C) 1.5 km/h (D) 2.5 km/h (E) 4 km/h

  1. A rubber ball is held motionless a height ho above a hard floor and released. Assuming that the collision withthe floor is elastic, which one of the following graphs best shows the relationship between the total energy E ofthe ball and its height h above the surface.
  1. Which of the following quantities is a scalar that is always positive or zero?

(A)Power (B) Work (C) Kinetic energy

(D) Linear momentum (E) Angular momentum

  1. Which of the following is true when an object of mass m moving on a horizontal frictionless surface hits andsticks to an object of mass M > m, which is initially at rest on the surface?

(A) The collision is elastic.

(B) All of the initial kinetic energy of the less massive object is lost.

(C) The momentum of the objects that are stuck together has a smaller magnitude than the initial momentum ofthe less-massive object.

(D) The speed of the objects that are stuck together will be less than the initial speed of the less massive object.

(E) The direction of motion of the objects that are stuck together depends on whether the hit is a head-oncollision.

  1. A solid metal ball and a hollow plastic ball of the same external radius are released from rest in a large vacuumchamber. When each has fallen 1m, they both have the same

(A) inertia(B) speed (C) momentum

(D) kinetic energy (E) change in potential energy

Questions 17-18

A student obtains data on the magnitude of force applied to an object as a function of time and displays the data onthe graph above.

  1. The slope of the “best fit” straight line is most nearly

(A) 5 N/s

(B) 6 N/s

(C) 7 N/s

(D) 8 N/s

(E) 10 N/s

  1. The increase in the momentum of the object between t=0 s and t=4 s is most nearly

(A) 40 N∙s

(B) 50 N∙s

(C) 60 N∙s

(D) 80 N∙s

(E) 100 N∙s

  1. How does an air mattress protect a stunt person landing on the ground after a stunt?

(A) It reduces the kinetic energy loss of the stunt person.

(B) It reduces the momentum change of the stunt person.

(C) It increases the momentum change of the stunt person.

(D) It shortens the stopping time of the stunt person and increases the force applied during the landing.

(E) It lengthens the stopping time of the stunt person and reduces the force applied during the

landing.

  1. An object having an initial momentum that may be represented by the vector above strikes an object that is initially at rest. Which of the following sets of vectors may represent the momenta of the two objects after the collision?

(A) v0/4(B) v0/2(C)√2*(v0/2)(D)√3*(v0/2)(E) v0

FRQ:

As shown above, a 0.20-kilogram mass is sliding on a horizontal, frictionless air track with a speed of 3.0meters per second when it instantaneously hits and sticks to a 1.3-kilogram mass initially at rest on the track. The1.3-kilogram mass is connected to one end of a massless spring, which has a springconstant of 100 newtons per meter. The other end of the spring is fixed.

a. Determine the following for the 0.20-kilogram mass immediately before the impact:

i. Its linear momentum ii. Its kinetic energy

b. Determine the following for the combined masses immediately after the impact:

i. The linear momentum ii. The kinetic energy

After the collision, the two masses compress the spring as shown.

c. Determine the maximum compression distance of the spring.