Question

Two forces, of magnitudes F1 = 80.0 N and F2 = 40.0 N , act in opposite directions on a block, which sits atop a frictionless surface, as shown in the figure. (Figure 1)Initially, the center of the block is at position xi = -4.00 cm . At some later time, the block has moved to the right, and its center is at a new position, xf = 5.00 cm .

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PART 1)

Find the work W1 done on the block by the force of magnitude F1 = 80.0 N as the block moves from xi = -4.00 cm to xf = 5.00 cm .

Express your answer numerically, in joules.

W1=

PART 2)

Find the work W2 done by the force of magnitude F2 = 40.0 N as the block moves from xi = -4.00 cm to xf = 5.00 cm .

Express your answer numerically, in joules.

W2=

PART 3)

What is the net work Wnet done on the block by the two forces?

Express your answer numerically, in joules.

Wnet=

PART 4)

Determine the changeKf−Ki in the kinetic energy of the block as it moves from xi = -4.00 cm to xf = 5.00 cm .

Express your answer numerically, in joules.

Kf - Ki =

Answer 1

a)

W1 = F1 ( xf - xi) = 80* ( 5 + 4)* 10^-2 = 7.2 J

b)

W2 = F2 ( xf - xi) = - 40 ( 5 +4) * 10^-2 = - 3.6 J

c)

net workdone

W = W1 + W2 = 3.6 J

d)

change in kE = net workone = 3.6 J

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