a reindeer pulls a sled....

man

2013-05-01 8:27 am

a reindeer pulls a sled with santa claus on it so that sled moves towards the left hand side at a constant velocity(Fig.2).the coefficient of dynamic friction between the sled and the ground is 0.01.

a.state the direction of fricition acting on the sled.compare,with explanation.the magnitude of the pulling force given by the reindeer and the weight of the sled together with the santa.

b.the bird from the sky is now landing on the shoulder of santa.explain the change of friction acting on the sled.

c.indicate the change of the coefficient of friction when the sled is now at resting state.compare the magnitude of the pulling force that moves the sled from at rest to the one that keeping the sled to move in Fig2.

回答 (1)

天同

2013-05-01 9:13 am

✔ 最佳答案

(a) Friction always opposes motion. Since the sled is moving towards the left, friction thus acts towards the right.

Friction Ff = 0.01 x normal reaction of sled and Santa
Hence, pulling force = Ff = 0.01 x weight of sled and Santa
The pulling force is 1/100 times the weight of the sled and Santa

(b) The bird's weight increases the normal reaction and hence the frictional force.

(c) In general, the coefficient of static friction is larger than that for dynamic friction. Hence, the force needed to pull the sled from rest is larger that that required to keep the sled moving at constant speed.

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