A weight lifter lifts a 410-N set of weights from ground level to a position ove

Question

A weight lifter lifts a 410-N set of weights from ground level to a position over his head, a vertical distance of 1.80 m. How much work does the weight lifter do, assuming he moves 738 J Starting from rest, a 4.20 kg block slides 2.30 m down a rough 30.0 degree incline. The coefficient of kinetic friction between the block and the incline is mu_k = 0.436. (a) Determine the work done by the force of gravity. 51.842 Your response is within 10% of the correct value. This may be due to roundoff error, or you could have a mistake in your calculation. Carry out all intermediate results to at least (b) Determine the work done by the friction force between block and incline. J (c) Determine the work done by the normal force. 0 J (d) Qualitatively, how would the answers change if a shorter ramp at a steeper angle were used to span the same vertical height? When a 3.00-kg object is hung vertically on a certain light spring described by Hooke's law, the spring stretches 0.04 cm. (a) What is the force constant of the spring? 967.105 N/m (b) If the 3.00-kg object is removed, how far will the spring stretch if a 1.50-kg block is hung on it? 1.52 cm (c) How much work must an external agent do to strech the same spring 7.50 cm from its unstretched position? 2.7199 J

Explanation / Answer

a) Verical height by which the mass slides = 2.3xsin30o =1.15m

Work done by force of gravity = 4.2x9.8x1.15 = 47.334 J

b)normal forfce exerted on mass = 4.2x9.8xcos30o = 35.64 N

coefficient of friction = 0.436

Frictional force = 0.436x35.64 = 15.54 N

Work done by frictional force = 15.54x2.3 = 35.742J

c) there is not displacement of the mass in the direction of normal force

Therefore, work done by normal force = 0

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