Physics 1

Homework #5

Due: March 3/4

Problem Solving Techniques:

  1. Visualize the problem.
  2. Identify what is known and unknown.
  3. Define the relationships that you know.
  4. Using 1 – 3, try to solve the problem.
  5. Does your answer make sense? If not, check your work.
  1. The force required to stretch a spring a distance d is directly proportional to d. A force of 11.2Newtons stretches a spring 36.1 cm. How much force is required to stretch the spring 50.0 cm?
  1. The distance that an object falls under the influence of gravity varies as the square of the time that the object is falling. A rocked dropped from the edge of a steep cliff travels 4.9 m after 1.1s. It hits the ground in 10.3 s, how high is the top of the cliff from the valley below?
  1. In Physics 11C or 5B, you’ll learn about resistors, devicesthat limit current flow. When current flows through a resistor, it gets hot. The thermal power (in Watts)given off by a resistor varies directly with its resistance (a property of the resistor itself, the unit of resistance is theohm) and with the square of the current (in Amperes) flowing through the resistor. A 12 ohm resistor carrying 1.2 Ampere of current generates 18 Watts of heat. If the current is increased to 9.4Amperes, how much heat is generated?
  1. In class we learned that the frequency of a vibrating string varies directly with the square root of the tension on the string. If a string vibrates at 321 Hz with a tension t on it, what is the string’s frequency if the tension is doubled?
  1. The Universal Law of Gravity states that the gravitational force between two objects varies directly as the mass of the object, directly as the mass of the second object, and inversely as the square of the distance between them. If the distance between two objects doubles, how does the force between them change?
  1. A moving object has a kinetic energy proportional to the square of its velocity. By what factor does the kinetic energy of a car change when its speed increase from 30 MPH to 70 MPH?