Solution_Problem_of_the_Week_6

Solution_Problem_of_the_Week_6 - final speed of the boat?...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Solution - Problem of the Week 6 Jack and Jill are maneuvering a 3000 kg boat near a dock. Initially the boat’s position is <2, 0, 3> m and its speed is 1.3 m/s. As the boat moves to position <4, 0, 2> m, Jack exerts a force < 400, 0, 200> N and Jill exerts a force <150, 0, 300> N. (a) How much work does Jack do? We will apply the Energy Principle. System: the boat. Surroundings: Jack and Jill interacting with the boat. In general, the Energy Principle states that Δ E sys = W = F i Δ r where the last equality holds for a constant force acting over the distance Δ r . In what follows Δ r = r f r i = 4,0,2 m 2,0,3 m = 2,0, 1 m The amount of work done by Jack is: F Jack i Δ r = 400,0,200 N i 2,0, 1 m = 800 200 = 1000 N m (b) How much work does Jill do? F Jill i Δ r = 150,0,300 N i 2,0, 1 m = 300 300 = 0 N m (c) Assuming that we can neglect the work done by the water on the boat, what is the
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: final speed of the boat? Applying the Energy Principle: E sys = KE = 1 2 M ( v f 2 v i 2 ) = F net i r = 1000 J Solving for the final speed, v f = 1.01 m / s (d) Without doing any geometrical calculations, say what is the angle between the (vector) force that Jill exerts and the (vector) velocity of the boat. Explain briefly how you know this. The (vector) velocity of the boat is along the displacement ( r ) direction. We have already found that Jill did no work in moving the boat from its initial position to its final position, yet she did exert a force. Therefore, the force Jill exerted is perpendicular to the boats velocity. (e) What effect does Jill have on the boats motion? While Jill does no work on the boat, she has changed its direction of motion....
View Full Document

This note was uploaded on 12/07/2011 for the course PHYS 172 taught by Professor ? during the Fall '08 term at Purdue University-West Lafayette.

Page1 / 2

Solution_Problem_of_the_Week_6 - final speed of the boat?...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online