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Chapter 7: Q. 32 (page 178)

Bob, who has a mass of, can throw a rock with a speed of 30m/s. The distance through which his hand moves as he accelerates the rock from rest until he releases it is 1.0m.

a. What constant force must Bob exert on the rock to throw it with this speed?

b. If Bob is standing on frictionless ice, what is his recoil speed after releasing the rock?

Short Answer

Expert verified

(a) The force Bob must exert on the rock to throw is 225N

(B) The recoil speed after releasing the rock is0.2m/s

Step by step solution

01

Given information (part a)

Mass of Bob,m=75kg

Weight of rock weight, m=0.5kg

Speed of the rock,30m/s

02

Explanation (part a)

Acceleration :

v2=u2+2asInitialvelocityu=0a=v2-u22sa=30m/s2-021ma=450m/s2

Force exerted on the rock

F=maF=0.5kg450m/s2F=225N

03

Given information (part b)

Mass of Bob, m=75kg

Weight of rock weight, localid="1649688983057" m=0.5kg

Speed of the rock,v=30m/s

04

Explanation (part b)

By conservation of momentum

m1v1+m2v2=0wherem1andv1arethemassandvelocityoftherock,m2andv2arethemassandrecoilvelocityofbob.Sincethespeedofrockisoppositetobob'srecoilspeedv1=-30m/s0.5kg-30m/s+75kgv2=0v2=0.2m/s

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Most popular questions from this chapter

Block Ain FIGUREEX7.4is heavier than block Band is sliding down the incline. All surfaces have friction. The rope is massless, and the massless pulley turns on frictionless bearings. The rope and the pulley are among the interacting objects, but you’ll have to decide if they’re part of the system.

A woman living in a third-story apartment is moving out. Rather than carrying everything down the stairs, she decides to pack her belongings into crates, attach a frictionless pulley to her balcony railing, and lower the crates by rope. How hard must she pull on the horizontal end of the rope to lower a 25kgcrate at steady speed?

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