chp. 7 #18 A tow truck pulls a car 5.10 km along a horizontal roadway using a ca

Question

chp. 7 #18

A tow truck pulls a car 5.10 km along a horizontal roadway using a cable having a tension of 910 N .

A) How much work does the cable do on the car if it pulls horizontally? (in J)

B) How much work does the cable do on the car if it pulls at 35.0 above the horizontal? (in J)

C) How much work does the cable do on the tow truck if it pulls horizontally? (in J)

D) How much work does the cable do on the tow truck if it pulls at 35.0 above the horizontal? ( in J)

E) How much work does gravity do on the car in part A? ( in J)

Explanation / Answer

In part (A), when the cable pulls horizontally theta = 0° and when it pulls at 35.0° above the horizontal  35.0°
. In part (C), if the cable pulls horizontally theta = 180° If the cable pulls on the car at 35.0° above the horizontal it pulls on the truck at 35.0° below the horizontal and theta = 145.0°
. For the gravity force theta = 90° since the force is vertical and the displacement is horizontal.

When the cable is horizontal,

W = (910 N)(5.10 *103 m)cos0 = 4.64*106 J

A>. When the cable is 35.0° above the horizontal,

B> W = (910 N)(5.10*103m)cos35 =  3.8 *106   J

C.D> cos180 = - cos0 and   cos145 = -cos35

, so the answers are -4.64*106 J and -3.8*106 J

.

(E) Since

cos(theta) = cos90 = 0

W = 0 in both cases.

If the car and truck are taken together as the system, the tension in the cable does no net work.

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