00 kg block slides with uniform acceleration on a horizontal surface for 5. The block’s kinetic energy strictly decreases from 50.0 J to 20.0 J in…

A 5.00 kg block slides with uniform acceleration on a horizontal surface for 5.00s. The block’s kinetic energy strictly decreases from 50.0 J to 20.0 J in this time. What is the average speed of the block during the motion described? Explain.