How to find average friction force?
2017-09-19 8:41 pm
A 0.5 kg block slides across a tabletop with an initial velocity of 20m/s and comes to rest in a distance of 70cm. How to find the average friction force that retarded its motion?
回答 (1)
2017-09-19 8:51 pm
Method 1 :
Work done by friction = loss in K.E.
f s = (1/2) m v²
f × (70/100) = (1/2) × 0.5 × 20²
f = 140 N (to 2 sig. fig.)
Average frictional force = 140 N
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Method 2 :
v² = u² + 2as
0 = 20² + 2 × a × (70/100)
a = -286 m/s²
f = m a = 0.5 × (-286) N = -140 N (to 2 sig. fig.)
Average frictional force = 140 N
Work done by friction = loss in K.E.
f s = (1/2) m v²
f × (70/100) = (1/2) × 0.5 × 20²
f = 140 N (to 2 sig. fig.)
Average frictional force = 140 N
====
Method 2 :
v² = u² + 2as
0 = 20² + 2 × a × (70/100)
a = -286 m/s²
f = m a = 0.5 × (-286) N = -140 N (to 2 sig. fig.)
Average frictional force = 140 N
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