Question

A man throws a boy throws the brakes to the height of 12 m, where they reach with the speed of 12 m per second. If he throws the brakes such that they just reach this height, then what percentage of energy will be saved?

(a) 0%
(b) 25%
(c) 50%
(d) 75%

Answer 1

The percentage of energy saved when the brakes are thrown to a height of 12 m is 0%.

Step-by-step explanation:

To determine the percentage of energy saved when the brakes on a boy are thrown to a height of 12 m, we can use the principle of conservation of energy. The potential energy of the brakes at the highest point can be calculated using the formula PE = mgh, where m is the mass, g is the acceleration due to gravity, and h is the height.

Since the brakes reach this height with a speed of 12 m/s, we can calculate their kinetic energy at the highest point using the formula KE = 0.5mv^2, where v is the velocity. The total energy of the system is equal to the sum of the potential and kinetic energy.

Let's assume the mass of the brakes is 1 kg. At the highest point, the potential energy is PE = (1 kg)(9.8 m/s^2)(12 m) = 117.6 J. The kinetic energy is KE = 0.5(1 kg)(12 m/s)^2 = 72 J. Therefore, the total energy of the system is 117.6 J + 72 J = 189.6 J.

Since the brakes were just thrown to reach this height, all of the energy is saved in the system. In other words, 100% of the energy is saved. Therefore, the correct answer is (a) 0%.