A boy on a skate board skates off a horizontal bench at a velocity of 10 m/s. One tenth of a second after he leaves the bench, to two significant figures, the magnitudes of his velocity and acceleration are: a) 10 m/s; 9.8 m/s2.
b) 9.0 m/s; 9.0 m/s2.
c) 9.0 m/s; 9.8 m/s2.
d) 1.0 m/s; 9.8 m/s2.
e) 1.0 m/s; 9.0 m/s2.

a) 10 m/s; 9.8 m/s²

Explanation:

After leaving the bench the boy undergoes a semi-projectile motion from top to bottom. Neglecting the effects of air friction, we can safely assume that the horizontal velocity remains constant throughout the motion. Thus, the magnitude of velocity is 10 m/s. The only acceleration in the boy is the acceleration due to gravity, due to free fall motion. Therefore, the magnitude of acceleration is 9.8 m/s².

Therefore, One tenth of a second after he leaves the bench, to two significant figures, the magnitudes of his velocity and acceleration are:

a) 10 m/s; 9.8 m/s²

the motion of a pendulum is a classic example of mechanical energy conservation. a pendulum consists of a mass (known as a bob ) attached by a string to a pivot point. as the pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion.

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