Arock hits the ground with a speed of 7 m/s and a kinetic energy of 100 j. what is the rock's mass?

Mass = (2*KE) / v²
∴ the answer is 200/49 

KE=1/2 times mass times velocity squared. So in this situation your equation would look like this 100J=1/2 times mass times 7 m/s^2. Your answer would be 4.0812 kg

Answer: it will take   4.36 seconds to reach her average velocity 10.69 miles/hour.explanation:   we have equation of motion ,where s is the displacement, a is the acceleration, u is the initial velocity and t is the time taken.average velocity = displacement/ time taken.average velocity = 10.69 miles/hr = 10.69*1.6*1000/(60*60) = 4.75 m/s4.75 = s/ts = 4. 1we also have acceleration = 2.18 m/s², initial velocity = 0 m/sso it will take   4.36 seconds to reach her average velocity 10.69 miles/hour.