Name (LAST, First) ______, ______

Date ___ / ___ / ______Block 1 2 3 4 5 6 7 8

Kinematics Review and Force Problems:

Work the following problems. The number in parenthesis preceding each problem is a reference for the teacher. The number(s) following some problems are answers. These answers do not necessarily have the correct number of significant digits. Drawing a free-body [force] diagram may help.

1.  (5.33) You drive a car for 2.0 h at 40 km/h, then for another 2.0 h at 60 km/h.

  1. What is your average velocity? (50)
  2. Do you get the same answer if you drive 100 km at each of the two speeds?
    Show your work. (No.)

2.  (5.49) A plane uniformly accelerates from 66 m/s to 88 m/s in 12.0 s. Determine:

  1. The displacement of the plane while accelerating. (920)
  2. The acceleration of the plane. (2)
  3. The force exerted on a 72.5 kg passenger. (130)

3.  (5.58) Rocket-powered sleds are used to test the responses of humans to acceleration. Starting from rest, one sled can reach a speed of 444 m/s in 1.80 s and can be brought to a stop again in 2.15 s. Assume the sled has a passenger with mass of 65 kg.

  1. Calculate the acceleration while the sled is speeding up. (250)
  2. Compare this starting acceleration to the acceleration due to gravity by determining the ratio [as a decimal, not a fraction] R = a/g. (25)
  3. Calculate the force exerted on the passenger by the sled. (2x104)
  4. Calculate the force exerted on the sled by the passenger.
  5. Repeat the above calculations for the period when the sled is slowing down. (-200, 20)
  6. Determine the displacements of the sled during both intervals. (400, 500)

4.  (6.23) A 65 kg swimmer jumps off of a 10.0 m tower. The swimmer comes to a stop 2.0 m below the surface. Determine the:

  1. Swimmer’s velocity on hitting the water. (-14)
  2. Acceleration of the swimmer while slowing in the water. (+50)
  3. Net force on the swimmer by the water while slowing. (+4000)
  4. Time intervals during both accelerations. (1.4, 0.3)

5.  (6.30) A horizontal force of 30.0 N is required to slide a 12.0 kg wooden crate across the floor at a constant velocity.
Hint: review http://www.physicsclassroom.com/Class/newtlaws/U2L2b.html
Determine the magnitude and direction of the:

  1. Gravitational force on the crate. (-200)
  2. Normal force exerted by the floor on the crate. (+200)
  3. Applied force on the crate. (30)
  4. Net force on the crate. (0)
    Hint: http://www.physicsclassroom.com/Class/newtlaws/U2L2d.html
  5. Frictional force exerted by the floor on the crate.


Calculate the:

  1. Acceleration of the box while moving? (0)
  2. Coefficient of kinetic friction between the crate and floor. (0.255)

6.  (6.37) A sled of mass 50.0 kg is pulled along flat, snow-covered ground. The static friction coefficient is 0.30, and the kinetic friction coefficient is 0.10. Calculate or determine the following:

  1. The weight of the sled. (500)
  2. The minimum force required to start the sled moving. (150)
  3. The minimum force required to keep the sled moving at a constant velocity. (50)
  4. Once moving, what total force must be applied to the sled to accelerate it at a rate of 3.0 m/s/s? (200)
  5. At what rate will the sled accelerate if the force required to start the sled moving [static] is applied while the sled is moving [kinetic]? (2)

7.  (6.39) A 65 kg boy and a 45 kg girl use an elastic rope while engaged in a tug-of-war on an icy, frictionless surface. The girl accelerates toward the boy at 3.0 m/s/s [relative to the ground]. Determine the:

  1. Force exerted by the girl on the rope. (135)
  2. Force exerted by the rope on the girl.
  3. Force exerted by the boy on the rope.
  4. Force exerted by the rope on the boy. (135)
  5. Magnitude of the acceleration [relative to the ground] of the boy toward the girl. (2.0)
  6. Magnitude of the acceleration [relative to the girl] of the boy toward the girl. (5.0)
  7. Weight of the girl. (440)
  8. Weight of the boy.
  9. Normal force on the girl.
  10. Normal force on the boy. (600)


The smooth, icy surface is replaced with a rough, icy surface. The coefficient of static friction is 0.24. Assume that the force(s) applied by the girl and boy remain constant.

  1. Calculate the friction force exerted on the girl’s feet by the icy surface.
  2. Will the girl move? Explain. Work is required.
  3. Will the boy move? Explain. Work is required.

The coefficient of kinetic friction is one-half the value of the coefficient of static friction. Assume that the force(s) applied by the girl and boy remain constant.

  1. Calculate the coefficient of kinetic friction. (0.12)
  2. Calculate the kinetic frictional force on both the boy and girl. (76, 53)
  3. Calculate the acceleration of the girl, relative to the ground. (1.8)
  4. Calculate the acceleration of the boy, relative to the ground. (0)
  5. A passing skater nudges the boy with enough force to break him free from the ice. Calculate his acceleration. (< 1)

Intro Problems (PPP) v07.doc 9/22/2008 1:13:00 PM Page 1 of 2