Question

A boy throws a ball of mass 0.25kg straight upward with an initial speed of 20m/s. When the ball returns to the boy, its speed is 17m/s. How much work does air resistance do on the ball during its flight?

a) 4.25 J
b) 8.50 J
c) 12.75 J
d) 17.00 J

Answer 1

The work done by air resistance on a ball thrown upwards and coming back down is represented by the loss of its kinetic energy, calculated based on the difference in the ball's initial and final velocities. The decrease in kinetic energy due to air resistance corresponds to 4.25 J of work done.

Step-by-step explanation:

The question deals with the work done by air resistance on a ball thrown upward and then falling back to the thrower. When an object moves through air, it experiences air resistance, which is a form of friction that does work on the object, thereby dissipating some of its mechanical energy as thermal energy.

The initial kinetic energy of the ball, when it is thrown upwards, can be calculated using the formula Kinetic Energy (KE) = 1/2 * m * v^2, where m is the mass of the ball and v is its initial velocity. When the ball returns back to the boy with a lower speed, it has lost some of its kinetic energy due to the work done by air resistance. The work done by air resistance (W_air) can be calculated as the difference in kinetic energy:

W_air = KE_initial - KE_final

Using the values from the question:

Initial KE = 1/2 * 0.25kg * (20m/s)^2 Final KE = 1/2 * 0.25kg * (17m/s)^2

By plugging in the values and calculating, we can find the work done by air resistance on the ball during its flight, which corresponds to option (a) 4.25 J, provided in the multiple-choice options.