A boy is sitting on a swing at a maximum height of 5m above the ground. When the

Question

A boy is sitting on a swing at a maximum height of 5m above the ground. When the swing passes through the mean position which is 2m above the ground, what will be his velocity at mean position? 1. 2. Water flows over a waterfall at the rate of 35000 kg per 50 min. How much power is generated 3. A 2kg block is dropped from a height of 0.4m on a spring of force constant 1960N/m. What will 4. If the original height of the rock is 3m. Calculate rock's speed when it has fallen to 1m above the . A 1000kg roller coaster moves from position 1to 2 then to position 3. by the falling water? be the maximum compression of the spring? ground. 1 15m

Explanation / Answer

(1) Initial height of the boy above the ground, h1 = 5 m

At the mean position, height of the boy above the ground, h2 = 2 m

So, loss in potential energy, PE = mgh1 - mgh2 = mg*(h1 - h2) = mg*(5 - 2) = 3mg

aThis loss in potential energy will be compensated by the gain in kinetic energy.

So, 3mg = (1/2)mv^2

cancel m from both sides-

3g = 0.5*v^2

=> v^2 = 6g = 6*9.81

=> v = 7.67 m/s

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