Question

A baby bird falls from its nest in a tree. Luckily, Sasquatch catches the baby bird before it hits the ground, bringing it to rest. Which describes the work W done by Sasquatch on the baby bird and its change in gravitational potential energy ∆Ugrav between the nest and where it was caught?
A. W > 0, ∆Ugrav < 0
B. W > 0, ∆Ugrav > 0
C. W = 0, ∆Ugrav > 0
D. W < 0, ∆Ugrav < 0

A 160.0 g hockey puck slides along an essentially frictionless ice rink with speed 4.70 m/s. A hockey player uses her stick to do 1.20 J of work on the puck. What is the puck’s speed after she has done this work??

A mover pushes a 50.0 kg couch with a 120.0 N horizontal force 4.00 m across a living room floor. What is the work done by the mover on the couch?

Answer 1

∆U = Uf-Ui

∆U = mg* ( hf -hi )

since Uf < Ui becuse final  heigh is less than initial height

A. W > 0, ∆Ugrav < 0

A 160.0 g hockey puck slides along an essentially frictionless ice rink with speed 4.70 m/s. A hockey player uses her stick to do 1.20 J of work on the puck. What is the puck’s speed after she has done this work

Work done = change in KE

1.20 = 1/2*0.160*(vf^2 -4.70^2)

1.2 = (1/2) 0.16 (v^2 - 4.7^2)

1.2 = 0.08 (v^2 - 22.09)

1.2 = 0.08 v^2 - 1.7672

from here vf ≈ 6.09016 m/s answer

A mover pushes a 50.0 kg couch with a 120.0 N horizontal force 4.00 m across a living room floor. What is the work done by the mover on the couch?

W = F*d =120*4 = 480 J answer