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# [help] mechanics - kinematics watch

1. a model car of mass 4 kg moves in straight line along horizontal ground. the resistance of the car has magnitude 4N.

i) the car batteries provide a constant power of 20 watts.

a) calculate the acceleration of the car at that instant when its speed is 2ms^-1 ?

b) when the car passes the point A, it is moving at a constat speed V ms^-1. show that V=5

ii) the car continues to move at 5ms^-1 until it reaches B at which point the batteries suddenly fail to provide power.
a) the car subsequently comes to rest at C. find the distance BC.
b) the time taken for the car to travel from A to C is 8 s . find the distance AB
2. i got my i) a) 1.25ms^-2 i duno if thats correct or not but how to do the rest actually ?

3. It'll be moving at a constant speed when the forces on it are equal. When does this happen?
4. b)P=Fv
F=4
v=20/4=5
5. ii)a)u=5, v=0
F=ma => -4=4a
a=-1

v^2=u^2 +2as
0=25 -2s
s=12.5m
6. 8- time taken from B to C= time from Ato B
a=(v-u)/t =>t=5s

from Ato B v is constant
v=s/t
5=s/3
s=15m
7. (Original post by *bobo*)
b)P=Fv
F=4
v=20/4=5
haha yeah my bro thought me this (damn how i could forget this simple formulae)
8. (Original post by *bobo*)
ii)a)u=5, v=0
F=ma => -4=4a
a=-1

v^2=u^2 +2as
0=25 -2s
s=12.5m

oh yeahhh i forgotten about the friction supposed to be oppostite to the direction of motion....thats why it is -4 rightt???

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