How far will it travel before it begins to fall to earth?

[robbie]

Please help. The first question I don' know how to solve for distance because I don't have time in the formula. I've spent three days, and my friends and I are stumped, and had no-where else to turn, someone please help me.

1. You shoot a 30g bullet straight up at a velocity of 724m/s. How far will it travel before it begins to fall to earth?

2. If your car can generate electricity 12 v AC at 50 amps and you decide to supply power to your home during a storm outage. Please design a transformer to convert electricity to 120 v AC. Your primary coil has 100 turns. What is the potential output from the transfer?

Thanks for any help!

 

[HallsofIvy]

1. You shoot a 30g bullet straight up at a velocity of 724m/s. How far will it travel before it begins to fall to earth?

You know that the acceleration due to gravity is -9.8 m/s² (negative since it is downward) so the speed at any time t is given by 724- 9.8t. The bullet will continue upward until its speed becomes 0. Then it will fall back as the speed becomes negative.

724- 9.8t= 0 gives t= 724/9.8= 73.9 seconds.

You also know that the height above the ground is given by (the "anti-derivative" of speed) 724t- 4.9t². Plug 73.9 seconds in for t and calculate the height at that time.

 

[physics247]

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2. If your car can generate electricity 12 v AC at 50 amps and you decide to supply power to your home during a storm outage. Please design a transformer to convert electricity to 120 v AC. Your primary coil has 100 turns. What is the potential output from the transfer?
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Are you being asked for power output?

Your max power output from the transformer is the power in.

Your secondary turns must be 10 times more than your primary turns since you are looking for 10 times the voltage output.

Your current output is therefore one-tenth your current input..