CP Physics
Practice Test
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See variable sheet
Examples of conservation of mechanical energy – A child going down a frictionless slide. An
arrow being shot in an environment without drag.
Work = F d cos 𝜃 is the overall formula for applied work. A specific application of that
formula is when changing the height of yourself or an object, such as the power lab. Notice for
work done against gravity the force is the weight (mass times acceleration due to gravity)
multiplied by the vertical displacement.
As with many examples in the class, the increased time to decelerate reduces the force of
impact. The impulse is the same, but having more time, reduces the force.
Watch the signs of the velocity. Draw a picture to help you. The impulse is 40 Newton seconds.
The contact force is 160 N.
Ok , you ‘ve seen this one before. Throw the camera away from the ship. It’s just like the kyack
problem.
Conservation of momentum problem. This this way when objects are colliding. 2.86 m/sec is
the final velocity.
(compare to number 7). Typo on practice. Kinetic energy before is 48 Joules. After it is 28.6
Joules. The energy is lost at impact, denting, sound, heat, etc.
12.1 m/s Conservation of mechanical energy problem
A. 10 m/s Conservation of mechanical energy.
B. The impulse if the vaulter sinks into the foam and doesn’t bounce off is 550 Newton
Seconds. This would make the contact force 1833 N. This seems high. The 0.3 seconds is
probably on the low side.
Johnnys work against gravity is 2400 Joules. The power is 343 Watts.
Sadly, 24,000 joules converted to Calories is 5.7
A tennis ball is going to give more impulse than a hacky sack.
If the velocity goes down by half, the kinetic energy goes down to ¼ of the original.