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Newton’s Second Law

Solve the following problems using what you know about Newton’s Laws and the four powerful equations. Be careful, some of the problems have multiple parts!

Kinematics Equations
1.) d = ½(v + v0)t
2.) d = v0t + ½at2
3.) v2 = v02 + 2ad
4.) v = v0 + at

Newton’s Laws
  1. An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
  2. The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.
    In terms of an equation, the net force is equal to the product of the object's mass and its acceleration.
    Fnet = m × a
  3. For every action, there is an equal and opposite reaction. That is, forces come in pairs.
  1. What acceleration will result when a 12-N net force applied to a 3-kg object? A 6-kg object? What velocity will the 6-kg object have after 10 s?
  2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s2. Determine the mass.
  3. An object is accelerating at 2 m/s2. If the net force is tripled and the mass is doubled, then what is the new acceleration?
  4. An object is accelerating at 2 m/s2. If the net force is tripled and the mass is halved, then what is the new acceleration?
  5. How much tension must a rope withstand if it is used to accelerate a 1250-kg car horizontally at 1.30 m/s2? Ignore friction.

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  1. A net force of 255 N accelerates a bike and rider at 2.20 m/s2. What is the mass of the bike and rider?
  2. What is the weight of a 58-kg astronaut:
    1. on Earth?
    2. on the Moon (g = 1.7 m/s2)?
    3. on Mars (g = 3.7 m/s2)?
    4. in outer space traveling at constant velocity?
    (answers will be in newtons (N))
  3. What is the average force required to stop a 1050-kg car in 7.0 s if it is traveling at 90 km/hr?
  4. What is the average force required to accelerate a 6.25-g pellet from rest to 155 m/s over a distance of 0.700 m along the barrel of a rifle?
  5. How much force is required to accelerate a 7.0-g object at 10,000 “g’s” (say, in a centrifuge)?
  6. A 873-kg dragster, starting from rest, attains a speed of 26.3 m/s in 3.9 s.
    1. Find the average acceleration of the dragster.
    2. What is the average force on the dragster during its acceleration?
    3. Assume the driver has a mass of 68 kg. What horizontal force does the seat exert on the driver? Express the acceleration she feels as a multiple of g.
    4. Draw a forces diagram for the dragster.
    5. Draw a forces diagram for the driver.
Last updated: Nov 09, 2006 Home