Review of simple concepts studied in the past: Gravitational Potential What is t

Question

Review of simple concepts studied in the past: Gravitational Potential What is the gravitational field strength at the earth's surface? How much work is required for a 100 kg man to climb a 7 meter tall ladder? How much potential energy does the man lose when falling off the top of the ladder? How much kinetic energy does the man have as he hits the ground after a 7 meter fal? If an entire classroom of 25 physics students (average mass 70 kg) climbs the ladder, how much energy is applied to the system? How much actual energy is required to send a 100 kg man into outer space (neglecting friction/etc)? Electrical Potential What is the electrical field strength measured 200 nanometers from a proton? How much work is required to bring two widely separated protons to positions 200 nanometers apart? Four distant protons are all brought into proximity of a fifth proton (from the top/bottom/left/right) and surround the fifth proton at a distance of 200 nanometers. If each of the four protons is positioned exactly opposite one of the other protons, what is the value of the electric force on the center/fifth proton?- What is the magnitude of E on the center/fifth proton? What is the the electrical potential of the fifth/center proton? A super-long metal rod contains an electrical charge density of 2.5 C/meter of length. What is the electrical field strength at a distance of 3 meters from the rod? What is the electrical potential at a distance of 3 meters from the rod? What is the electrical potential at a distance of 3 meters from super-huge metal sheet containing a charge of 2.5uC/m2?

Explanation / Answer

1). The gravitational field strength on earth's surface is 10 N/kg ( force per unit mass)

2) Work done is equal to potential energy gained = 6860 JOULES

3) Potential energy at the top of ladder is given as m*g*h = 100*9.8*7 = 6860 joules. At the bottom of the fall, potential energy decreases to zero. Therefore, person loses 6860 joules of potential energy.

4) time to fall 7 meters is given as 7 = 1/2*9.8*t2 ( from kinematics)

t = 1.195 seconds

thereofore, velocity just before touching the ground is v = at = 11.71 m/s

thereofore, kinetic energy = 0.5*100*11.712 = 6859 joules. As we can notice, it is same as the potential energy at the top. it means as the person falls, the potential energy gets converted to kinetic energy . Hence,, it proves conservation of energy. .  

5) Just find out the total mass and apply the potential energy formula to get the result.

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