Test 3. Potential and kinetic energy. Momentum. Torque. Student\'s name :hAas in

Question

Test 3. Potential and kinetic energy. Momentum. Torque. Student's name :hAas in Looe Assigned: March 28, 2018 1. Potential and kinetic energy a) What is the change in the potential energy of a dumbbell of mass m-5 kg, when a person lifts it up from the floor to the height of h-2 m? Assume that the reference level for zero potential energy is the floor level. (12 pts.) b) What is the maximum velocity that the dumbbell will reach during free fall, starting from initial height h-2 m, if its initial velocity is zero? Calculate it using the energy conservation law. (13 pts.)

Explanation / Answer

1. (a)

change in potential energy = V_f - V_i

where  V_f = Final potential energy , V_i = initial Potential energy.

change in potential energy = m.g.h - 0 (due to reference level)

=5*9.8*2 kg.m^2/sec^2

=98  kg.m^2/sec^2

(b).

change in K.E. = change in P.E.

(m.v_f^2)/2 - (m.v_i^2)/2 = 98 ----------(i)

where v_f = final velocity, v_i = initial velocity.

v_i=0 (given)

v_f = 6.26 m/sec.

I just write down the velocity without calculation , you can verify this using the above equation (i).

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