Question

Monica pulls her daughter Jessie in a bike trailer. The trailer and Jessie together have a mass of 25 kg. Monica starts up a 100-m-long slope that's 4.0 m high. On the slope, Monica's bike pulls on the trailer with a constant force of 7.0 N. They start out at the bottom of the slope with a speed of 5.6 m/s.

What is their speed at the top of the slope? Express your answer with the appropriate units.

Answer 1

Kinetic energy at bottom of incline KE1=m/2=25X/2=392Joule (u=initial velocity=5.6m/s, m=mass=25kg)

Work done on incline   W=FXS=7X100=700Joule    (F=force=7N, S=displacement=100m=length of incline)

Potential energy at top of incline   PE=mgh=25X9.8X4=980joule     (g=9.8m/s2, h=height of incline=4meter)

Kinetic energy at top     KE2=m/2    

v=velocity at top=?

By conservation of energy,

KE1+W=PE+KE2

392+700=980+KE2

KE2=1092-980=112

m/2 =112

=112X2/m=112X2/25=8.96

v=2.99m/s=3m/s=velocity at top