Physics 111 hw#2

Due Friday, 27 May 2016

ASV-03. On a 20-mile bike ride, you ride the first 10 miles at an average speed of 8 mph.

a) What must your average speed over the next 10 miles be to have your average speed for the total 20 miles be 4 mph?

b) What must your average speed over the next 10 miles be to have your average speed for the total 20 miles be 12 mph?

c) Given this average speed for the first 10 miles, can you possibly attain an average speed of 16 mph for the total 20-mile ride? Explain.

ASV-04. In a relay race, each contestant runs 25.0 m west while carrying an egg balanced on a spoon, turns around, and goes back to the starting point. Edith runs the first 25.0 m in 20.0 s. On the return trip she is more confident and takes only 15.0 s.

a) What is the magnitude of her average velocity for the first 25.0 m?

b) What is the magnitude of her average velocity for the return trip?

c) What is her average velocity for the entire round trip?

d) What is her average speed for the round trip?

ASV-05. You travel E for 100 m at 7 m/s. Then you travel in a path that makes a semicircle of radius 50m with a speed of 5 m/s, as shown in the diagram. Find your average speed and velocity for this trip.

AA-01. An astronaut has left the International Space Station to test a new space scooter. His partner measures the following velocity changes, each taking place in a 10-s interval. What are the magnitudeand the direction of the average acceleration in each interval? Assume that the positive direction is to the right.

a) At the beginning of the interval the astronaut is moving toward the right along the x-axis at 15.0 m/s, and at the end of the interval he is moving toward the right at 5.0 m/s.

b) Beginning: to left at 5.0 m/s. End: to left at 15.0 m/s.

c) Beginning: to right at 15.0 m/s. End: to left at 15.0 m/s.

AA-01A. You travel in a curve, tracing out ¼ of a circle of radius 30m as shown in the diagram at right. At the start, you are going 1 m/s north. At the very end, you are going 6 m/s east. The whole trip took 4.5 seconds. For this trip, determine

a)the path length;

b)the displacement;

c)the average speed;

d)the average velocity;

e)the average acceleration.

f)Note that the average speed is greater than 6 m/s. Explain how this is possible.

RA-03. (Young & Friedman 11th ed. Ex. 3.33-4) A Ferris wheel with radius 14m is turning about a horizontal axis through its center. The linear speed of a passenger on the rim is constant and equal to 7.00 m/s. What are the magnitude and direction of the passenger’s acceleration as she passes through

a) the lowest point in her circular motion?

b) the highest point in her circular motion?

c) How long does it take the Ferris wheel to make one revolution?

RV-04. (Young & Friedman 11th ed. Ex. 3.40) An airplane pilot wishes to fly due west. A wind of 80.0 km/h is blowing toward the south. The airspeed of the plane (its speed in still air) is 320.0 km/h. Use a vector diagram to help you answer the following.

a)What direction should the pilot head?

b)What is the speed of the plane over the ground?

RV-05. (Young & Friedman 11th ed. Prob. 3.85) In a World Cup soccer match, Juan is running due north toward the goal with a speed of 8.00 m/s relative to the ground. A teammate kicks the ball in such a way that it travels at a speed of 12.0 m/s moving in a direction 37.0o E of N relative to the ground. What are the magnitude and direction of the ball’s velocity relative to Juan?

“Bike Flag” Big Jim is riding his Harley towards the north on a long straight road at 25 mph. A stiff wind blows out of the SW (towards the NE) at 20 mph. What direction (exact angle) will the flag that sits on the end of a long pole attached to his bike point?

(over)