Chapter 8

 

  1. (p.204 prob.76) A 0.20-kg pinecone falls from a branch 18m above the ground. (a) With what speed would it hit the ground if air resistance could be ignore? (b) If it actually hits the groound with a speed of 10.0m/s, what was the average force of air resistance exerted on it?

    Answer.

  2. (p.204 prob.81) A65-kg hiker climbs to the top of a 3900-m-high mountain. The climb is made in 5.0h starting at an elevation of 2200m. Calculate (a) the work done by the hiker against gravity, (b) the average power output in watts and in horsepower, and (c) assuming the body is 15% efficient, what rate of energy input was required.

    Answer.

  3. (p.205 prob.90) A 20-kg sled starts up a 30° incline with a speed of 2.4m/s. the coefficient of kinetic friction is mk = 0.25. (a) How far up the incline does the sled travel? (b) What condition must you put on the coefficient of static friction if the sled is not to get stuck at the point determined in (a) part? (c) If the sled slides back down, what is its speed when it returns to its starting point?

    Answer.

  4. (p.205 prob.95) As a city engineer, you need to estimate the power required to pump water from a new well. the well is 400m deep and the estimated demand is 1,000,000kg per day. The pump motor is about 80% efficient in converting electrical energy to mechanical energy.

    Answer.

  5. *(p.205 prob.89) The nuclear force between two neutrons in a nucleus is described roughly by the Yukawa potential

                                    U(r) = - U0(r0/r)e-r/r0

    where r is the distance between the neutrons and U0 and r0(»10-15m) are constant. (a) determine the force F(r). (b) What is the ration F(3r0)/F(r0)? (c) Calculate this same ratio for the force between two electrically charged particles where = -C/r, with C a constant. Why is the Yukawa force referred to as a "short-range" force?

    Answer.

     

    SEND QUESTIONS