# pyhsic question for count iblis

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A 15 kg, 1m wide door which has frictionless hinges is closed but unlocked. A 400 g ball hits the exact middle of the door at a velocity of 35 m/s and bounces off elastically, thereby causing the door to slowly swing open. How long in seconds does it take for the door to fully open (rotate 90 degrees)?

• pyhsic question for count iblis -

The answer I posted was correct as far as I can see, the problem may well be a typo in the problem itself, e.g. a 400 gram ball slamming into the door at the speed of a speeding car is not going to "slowly" open the door.

Anyway, it's a complete waste of time to e.g. try to see if what was meant is 3.5 m/s. I would suggest forgetting about this problem and moving on to another problem, you simply say that you did the problem correctly, that the teacher made a mistake and that you demand full marks for this problem.

• pyhsic question for count iblis -

iblis got the problem right. for those trying to use jiskha to cheat on the brilliant problems, there was a mistake made in the acceptable answers for this week's question.

• pyhsic question for count iblis -

ibis ,I beg to differ,the door slowly open because the ball bounces back elastically,please don't be certain,when u are wrong

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