PHYS 2001 SI Week 8 Session 2PHYS 2001


Work, Energy, Impulse, & Momentum

  1. During a certain time interval, a 20-N object free-falls 10 meters. The object gains _____ Joules of kinetic energy during this interval.

a)10

b)20

c)200

d)2000

  1. Use the diagram below to answer questions 10-13: neglect any resistance forces (the system is conservative).
  1. As the object moves from point A to point D across the surface, the sum of its gravitational potential and kinetic energies ____.

A. decreases, only / B. decreases and then increases
C. increases and then decreases / D. remains the same
  1. The object will have a minimum gravitational potential energy at point ______.
  2. The kinetic energy at point C is less than the kinetic energy at point(s):

a)A and B

b)B only

c)D & E

d)A, D, & E

e)A only

  1. If the velocity at point B is 37.0 m/s, and the potential energy at point B is zero, then from what height did the object initially start?—
  1. While a person lifts a book of mass 2kg from the floor to a tabletop, 1.5m above the floor, how much work does the gravitational force do on the book?

a)-30J

b)-15J

c)0J

d)15J

e)30J

  1. A person who normally requires 12,000 kJ of food energy per day consumes 13,000 kJ of food per day, he will steadily gain weight.

a)How much time bicycling is required to work off this extra 1000 kJ if bicycling consumes 400 Watts of power?

  1. Determine which statements are true and which are false:

a)A large force always produces a larger impulse on a body than a smaller force.

b)If two particles of different masses have equal kinetic energy they also have equal momentum.

c)The linear momentum of an object is proportional to the mass of the object.

d)The kinetic energy is always conserved both in elastic collisions and inelastic collisions.

e)If the kinetic energy of a single particle is zero, its momentum must be zero.

f)If the momentum of a single particle is zero, its kinetic energy may not be zero.

  1. A man pushes a box with a net force of 500 N for a duration of 3.5 seconds. What is the change in momentum of the box?
  2. An astronaut in a space suit is motionless in outer space. The propulsion unit strapped to her back ejectssome gas with a velocity of 50 m/s. The astronaut recoils with a velocity of 1.0 m/s. If the mass of the astronaut and space suit after the gas is ejected is 120 kg, the mass of the gas ejected is

a)1.0 kg.

b)1.9 kg.

c)2.4 kg.

d)3.00 kg.

e)3.6 kg.

  1. A 1200 kg car travels at 25.0 m/s and collides head-on in a perfectly inelastic collision with a stationary 2400 kg truck. The kinetic energy lost in the collision is

a)330,000 J.

b)250,000 J.

c)125,000 J.

d)95,000 J.

e)75,000

  1. An object which weighs 10 N is dropped from rest from a height of 4 meters above the ground. When it has free-fallen 1 meter its total mechanical energy with respect to the ground is ____.

a. 2.5 J / b. 10 J / c. 30 J / d. 40 J
  1. A 740.0 N man, carrying a 1.7 kg rock, stands at the center of a frozen pond of radius 6.0 m. He is unable to get to the other side since there is no friction at all between his shoes and the ice. To overcome his difficulty, he throws the rock horizontally at a speed of 5.0 m/s toward the east shore.

a)What is the initial momentum of the system?

b)What velocity will the man be traveling after the rock is thrown?

c)What distance must he travel to reach the west shore?

d)How much time does it take him to reach the west shore?

  1. A 500-gram cart rolls with negligible friction along a straight flat track until it collides with a 750-gram cart that was initially at rest. Position-time data for the 500-gram cart before it hits the other cart is recorded in the data table below.

a.)At time t = 2 seconds, the two carts collide in a perfectly inelastic collision. Calculate the final velocity of the 500-gram cart after this collision.

b.)How much mechanical energy was converted into heat during the collision (lost)

1