Velocity=3.4m/sec
Mass=30kg
so kinetic energy=1/2mv^2
=1/2×30×3.4×3.4
=15×3.4×3.4
=15×11.56
=173.4 kg m per second square
In the 4.10 seconds that elapsed, Ben reaches a velocity of


In this time, his displacement
satisfies


Momentum = (mass) x (speed)
Original momentum = (700 kg) x (30 m/s) = 21,000 kg-m/s
Final momentum = (700 kg) x (15 m/s) = 10,500 kg-m/s
Change in momentum = - 10,500 kg-m/s .