f.4 physics questions(force)

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[匿名]

2012-03-25 11:11 pm

1.a load of mass 15kg is pushed on a horizontal floor with a horizontal force of 50N. the load moves at a constant speed of 2m/s
a)find the friction
b)find the power given to overcome the friction
2.a car of mass 1500kg travels up a slope at constant speed of 8m/s. the slope makes an angle of 10 with the horizontal .the resistance acting on the car is 250N
a)what is the force exerting by the engine?
b)find the power output by the engine

更新1:

3. two blocks P of mass 5kg and Qof mass 3kg are connected by a light and non-extensible string passing over a light and smooth pulley.P is released from rest and moves on a rough horizontal surface when P has moves 2m, find a)work done against friction b)loss in potential energy of Q c)speed of Q

回答 (2)

天同

2012-03-26 3:36 am

✔ 最佳答案

1.(a) Friction = applied force = 50 N
(b) Power = 50 x 2 = 100 w

2.(a) Force exerted by the engine
= (1500g.sin(10) + 250) N = 2855 N
where g is the acceleration due to gravity, taken to be 10 m/s2

(b) Power developed by yhe engine = 2855 x 8 w = 22,838 w

3. Is there any diagram given?
It seems there is not sufficient data to do the calculation.

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gogobb

2012-03-26 3:19 am

1a) Because the load is moving at constant speed, by Newton's 1st law, there is no net force acting on it. Therefore the frictional force = 50N (in opposite direction with the horizontal force)
1b) Power= W/t, i need the time taken and the displacement of the load to calculate power.
2a) Because the car is moving at constant speed, by Newton's 1st law, there is no net force acting on it. Therefore the force exerted by engine= 250N (in opposite direction with the resistance)
2b) Once again i need the time taken and the displacement of the car to calculate power
3a) F=ma=(5+3)(10)= 80N <- 10 is acceleration due to gravity
W=Fs=80(2) = 160J

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