Physics problem!!

I would be grateful on how to go aobut this problem:

A car has been caught in a box junction by police and you need to contest that you couldn't have stopped before entering it. I have the following info:

Width of junction: 8m
Time orange light displayed: 3s
Speed Limit: 30mph
Car length: 2m

I'm taking for fact that the car has 120 horsepower=90 kW
and that the car weighs 1000kg

I'd be grateful for any help.

Reply 1

elpaw

u=30mph = 30*8/5 = 48 km/h = 48000/3600 = 13.3 m/s
v=0
KE of car = .5mv^2 = .5(1000)(13.3)^2 = 88888.888888888...... J

=> time taken to stop = KE/P = 0.99 s

=> he could have stopped within 3s of seeing the amber light.

but it depends on where he started. if the light changed amber while he was entering the junction, he would have entered it anyway.

Reply 2

not1

elpaw

=> time taken to stop = KE/P = 0.99 s

explain elly

Reply 3

elpaw

edders

explain elly

p = E/t => t = E/p

Reply 4

not1

elpaw

p = E/t => t = E/p

ah of course. 1second seems too short to me though, 2 sec more like with good brakes and an emergency stop lol

Reply 5

Saf!

can any1 answer this biology 1:

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