Physics I  Review Outline for Test II

Oct. 10, 2005 - updated for 2005

Radioactivity

• G-M Tube - how it works
• Nature of radioactivity - half-life
• Simulation of decay using dice
• Exponential function: R = R₀e^(-lt)
• Analysis of decay curve using natural log
• Calculate half-life from decay constant
• Practice problems:
1. The half-life of an element is 5 year.  Calculate the decay constant in year^-1
2. How many decays per sec. occur for a gram of radium  ²²⁶Ra which has a half-life of 1620 year?

Force and Motion

• Newton's IInd Law:  a = F/M
• Newton of force :   1N = 1kg x 1 m/sec²
  
• Experiment to measure force and accel to calculate mass - "Shove it"
• Inertial mass and gravitational mass
  
• What happens when total force = zero as in dual-fan cart?  (accel = zero; velocity = const)
• Falling feather friction is equal and opposite gravitational force (accel = zero)  (Total force = zero)
  
• Hanging masses and pulley - explain the resultant tension in the string
• Practice problems:
1. A 0.1 kg beach ball is falling in the air.  The friction force is 0.5 N directed upwards.  Calculate the ball's acceleration.
2. A 1500 kg automobile can accelerate from 0 to 25 m/s in 12 sec.  Calculate the force on the car.

Gravity and projectile motion

• Why do different mass objects fall at same rate with no friction? - This was largly missed in the lab reports.  See PPOW for Sept. 30, 2005.
  
• In a toss-up problem, what quantity remains constant?  What quantity(ies) is(are) zero at the apex of the toss?
• How to analyze for the acceleration?
• How to describe a trajectory?
• Pop-up ball launched from moving cart - explain why the ball lands in the cup
  
• Practice problems:
1. A ball is tossed with an initial velocity of 8 m/s elevated 60 degrees to the horizontal.  Calculate the initial vertical and horizontal velocities.  How long is the object in the air?
2. A ball is shot straight up from a moving vehicle.  Ignore air resistance.  The vehicle travels horizontally with a speed of 3.0 m/s.  The vertical initial speed is 6.0 m/s.  Calculate the vector velocity when the ball is at the peak of the trajectory.  How long does it take for the ball to reach the top?

Circular Motion

• Explain why an object travelling with a constant speed in a circle can have acceleration.
• Derive the expression for centripetal acceleration in terms of speed v and radius R.
• Explain the experiment with the whirlygig apparatus.
1. How is velocity measured
2. How is static force measured
3. Why are they equal?
• Practice problems:
1. 5 sec is required for an object to make 4 complete revolutions in a circle.  Calculate the period.
2. The moon orbits the earth in an orbit (R = 384 x 10³ km) with a period of 29 days.  Calculate the centripetal acceleration in m/s².
3. Calculate the centripetal force on a car traveling 40 m/s around a curve whose radius is 10 m if the car has a 1500 kg mass.  What provides this force?

Vernier Caliper - you will be given an object to measure to the nearest 0.1 mm.