p05_026.pdf

26. We assume the direction of motion is + x and assume the refrigerator starts from rest (so that the speed

being discussed is the velocity v which results from the process). The only force along the x axis is the

x component of the applied force F .

(a) Since v 0 =0, the combination of Eq. 2-11 and Eq. 5-2 leads simply to

F x = m v

⇒

v i = F cos θ i

for i =1 or 2 (where we denote θ 1 =0and θ 2 = θ for the two cases). Hence, we see that the ratio

v 2 over v 1 is equal to cos θ .

(b) Since v 0 =0, the combination of Eq. 2-16 and Eq. 5-2 leads to

F x = m v 2

2∆ x

⇒

v i =

2 F cos θ i

∆ x

for i =1 or 2 (again, θ 1 =0a nd θ 2 = θ is used for the two cases). In this scenario, we see that the

ratio v 2 over v 1 is equal to √ cos θ .