# physics problem 4

Problems:

Problem 1 (3 points):

A team of eight dogs pulls a sled with waxed wood runners on wet snow (mush!). The dogs have average masses of 19.0 kg, and the loaded sled with its rider has a mass of 210 kg.

(a) Calculate the acceleration starting from rest if each dog exerts an average force of 185 N backward on the snow.

(b) What is the acceleration once the sled starts to move?

(c) For both situations, calculate the force in the coupling between the dogs and the sled.

(coeff of Static friction = 0.14, coeff of kinetic friction = 0.1)

Problem 2 (4 points):

At takeoff, a commercial jet has a 60.0 m/s speed. Its tires have a diameter of 0.850 m.

(a) At how many rev/min are the tires rotating?

(b) What is the centripetal acceleration at the edge of the tire?

(c) With what force must a determined 1.00x 10-15kg bacterium cling to the rim?

(d) Take the ratio of this force to the bacterium’s weight.

Problem 3 (4 points):

Riders in an amusement park ride shaped like a Viking ship hung from a large pivot are rotated back and forth like a rigid pendulum. Sometime near the middle of the ride, the ship is momentarily motionless at the top of its circular arc. The ship then swings down under the influence of gravity.

(a) Assuming negligible friction, find the speed of the riders at the bottom of its arc, given the system’s center of mass travels in an arc having a radius of 14.0 m and the riders are near the center of mass.

(b) What is the centripetal acceleration at the bottom of the arc?

(c) Draw a free body diagram of the forces acting on a rider at the bottom of the arc.

(d) Find the force exerted by the ride on a 60.0 kg rider and compare it to her weight.