Force & Mass

Problems

practice

  1. A supertanker doesn't come with brakes. Using engines alone, it takes a loaded supertanker 13 km (8 miles) to stop. A typical vessel of this class has a gross mass of about 150 million kilograms (150 thousand tons) and a cruising speed of 50 kph (30 mph). Determine the average stopping force applied to the ship.
  2. Jump off the force plate demo
  3. Write something different.
  4. Write something completely different.

numerical

  1. Before a transparent material can be approved for use as a windshield in an airplane, it must first pass the "bird-impact resistance" test. A genuine (dead) or artificial chicken is accelerated to aircraft cruising speeds from the mouth of an air cannon and aimed at the windshield prototype. If the material shows any significant form of damage it fails the test. Each part of this problem contains an except from a USAF News Agency report.
    1. "Aircrews … find nothing funny about bird strikes. A strategically placed feathered bullet can wreak the same amount of damage as a laser-guided missile. The impact of a four-pound bird at 500 mph lasts less than a thousandth of a second, but can generate forces exceeding 100,000 pounds." Verify this statement; that is, that show that such a collision would indeed exert the force claimed.
    2. "They fire gelatin-molded, artificial birds weighing four pounds apiece, out a compressed air, 30 foot barrel cannon, which can shoot at speeds up to 900 mph. Three lasers and photodetectors measure the artificial chicken's velocity, while three cameras shoot the impact at 6,000 frames per second." Calculate the force exerted by the cannon on the chicken.
  2. An 11.3 g bullet leaves the muzzle of a 61 cm rifle with a horizontal velocity of 922 m/s. It strikes a target 457 m away with a horizontal velocity of 650 m/s. Determine …
    1. the acceleration of the bullet in the rifle
    2. the force of the propellant on the bullet in the rifle
    3. the horizontal acceleration of the bullet after it left the rifle barrel
    4. the aerodynamic drag on the bullet after it left the rifle barrel
    5. the time it took the bullet to travel the distance between the muzzle and the target
    6. how far the bullet fell by the time it hit the target
  3. The T-38 Talon is a small (14 × 4 × 8 m), lightweight (4000 kg), twin-engine, high-altitude, supersonic jet used by various US Department of Defense groups and NASA for training purposes.
    1. A T-38 requires 6670 N of thrust to fly at a constant horizontal velocity 300 m/s. Determine the following quantities for the T-38 at this moment …
      1. the weight
      2. the lift provided by the wings
      3. the aerodynamic drag
    2. The pilot has been instructed to accelerate horizontally at 0.10 g. Determine …
      1. the new thrust of the engines (assuming the drag remains constant)
      2. the time it takes to reach 360 m/s
  4. The table below shows some of the best and worst performing cars in an emergency braking test.
     
      weight/mass initial speed braking distance
    make and model (lb) (kg) (mph) (m/s) (ft) (m)
    Mercedes-Benz E550 Coupe 3810 1728 80 35.8 252 76.8
    Porsche 911 GT3 3075 1395 80 35.8 186 56.7
    Volkswagen Golf GTI 3-dr 3370 1529 60 26.8 143 43.6
    Alfa Romeo 8C Competizione 3495 1585 60 26.8 105 32.0
    Source: "Road Test Summary." Road & Track. (September 2010).
     
    1. For all four cars, determine the …
      1. braking acceleration
      2. braking force
    2. Which car is "the best"? Why did you choose this car?

statistical

  1. lab-f.txt
    A group of physics students measured the acceleration of a laboratory cart pulled across a table by a string tied to a falling weight. They varied the weight on the string, but kept the total mass of the system constant. Perform a linear fit on this data and use the slope to determine the mass of the system.
  2. lab-m.txt
    A group of physics students measured the acceleration of a laboratory cart pulled across a table by a string tied to a falling weight. They varied the mass of the cart, but kept the weight on the end of the string constant.
    1. Transform the data so that a linear fit can be performed.
    2. Use the slope to determine the net force on the system.
    3. The students performing this experiment used standard laboratory weights. What is the most probable mass of the weight on the end of the string?

The Physics Hypertextbook

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