Force and Motion (F.4)

👨🏻‍🏫 學術台其他 - 科學

Cham

2007-04-15 7:43 pm

A man is pulling a block of 10kg from rest with 80N up an inclined road. The length of the road is 10m and friction acting on the block is 10N. The angle is 30 degree.
How much time does the man take to pull the block to the top?

更新1:

Also, find the gain in the kinetic energy of the block when it reaches the top of the road.

回答 (1)

Karen

2007-04-15 8:18 pm

✔ 最佳答案

net Force=80-mgsin30度(地心吸力令物體下斜的力)-friction
=80-50-10
=20N
By F=ma
20N=10a
a=2ms^-2
The length of the road is 10m s= 10 , a =2
s=ut+1/2at^2
10=0t+1/2*2*t^2
t=開方10
=3.16s (3 sig fig)
At the top of the road , v = u+at = 0+2*開方10 =2開方10
KE = 1/2mv^2 =1/2*10*(2開方10)^2 = 200j
since the block was at rest , so the initital KE = 0
gain in KE = 200-0 = 200j

參考: my physic knowlege

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