A student must determine the effect of friction on the mechanical energy of a small block as it slides up a ramp. The block is launched with an initial speed vg from point A along a horizontal surface of negligible friction. It then slides up a ramp, where friction is not negligible, that is inclined at angle with respect to the
horizontal
, as shown in the figure. The student measures the maximum vertical height h attained by the block while on the ramp, labeled as point B in the figure. At
point B, the block comes to rest. The student performs three trials with the ramp at different angles, launching the block at the same initial speed vo for each trial.
The results from the trials are displayed in the table.
Consider the trial with the 45" ramp. Suppose the block is launched up the ramp such that it comes to rest at point B and then travels down the ramp. Which of the
following best describes the block's kinetic energy KA when it again reaches point A at the bottom of the ramp in comparison to the initial kinetic energy K, before
it travels up the ramp?
A KA > Ko, because the object will have a higher speed at the bottom of the ramp after sliding down the ramp than its original launch speed.
B
KA ramp.
C KA = K , because the law of the conservation of energy states that mechanical energy must be conserved for a closed system.
D
It is impossible to predict how the kinetic energy of the block at point A will compare to the original kinetic energy without knowing the magnitude
of the force of friction that is exerted on the block as it travels up and back down the ramp.