A 2.1 kg breadbox on a frictionless incline of angle ? = 44 ? is connected, by a

Question

A 2.1 kg breadbox on a frictionless incline of angle ? = 44 ? is connected, by a cord that runs over a pulley, to a light spring of spring constant k = 100 N/m, as shown in the figure. The box is released from rest when the spring is unstretched. Assume that the pulley is massless and frictionless. (a) What is the speed of the box when it has moved 10.7 cm down the incline? (b) How far down the incline from its point of release does the box slide before momentarily stopping, and what are the (c) magnitude and (d) direction of the box's acceleration at the instant the box momentarily stops?

I got a) 0.95 & b) 0.29 correct, but I put 7 for c and its wrong.

A 2.1 kg breadbox on a frictionless incline of angle ? = 44 ? is connected, by a cord that runs over a pulley, to a light spring of spring constant k = 100 N/m, as shown in the figure. The box is released from rest when the spring is unstretched. Assume that the pulley is massless and frictionless. (a) What is the speed of the box when it has moved 10.7 cm down the incline? (b) How far down the incline from its point of release does the box slide before momentarily stopping, and what are the (c) magnitude and (d) direction of the box's acceleration at the instant the box momentarily stops? I got a) 0.95 & b) 0.29 correct, but I put 7 for c and its wrong.

Explanation / Answer

part C:

When the eenrgy is = Loss of PE, the box stops

so 0.5 kx^2 = mgx/sin 44

x = 2 * mg/(k sin 44)

x = 2* 2.1 * 9.8/(100 * sin 44)

x = 0.59 m   or   59.25 cm

downward direction

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