Question

A 49 kg pole vaulter running at 10 m/s vaults over the bar. Her speed when she is above the bar is 0.7 m/s. The acceleration of gravity is 9.8 m/s2. Find her altitude as she crosses the bar. Neglect air resistance, as well as any energy absorbed by the pole.

Answer 1

Answer:

Height will be 5.127 m

Explanation:

We have given mass m = 49 kg

Speed over the bar v = 10 m /sec

Acceleration due to gravity $g=9.8m/sec^2$

Kinetic energy on the ground $=\frac{1}{2}mv^2=\frac{1}{2}\times 49\times 10^2=2450J$

Potential energy on the ground $=mgh=0$ (as height will be zero )

Speed above the bar = 0.7 m /sec

So kinetic energy above the bar $=\frac{1}{2}mv^2=\frac{1}{2}\times 49\times 0.7^2=12J$

Potential energy above the bar = mgh

From energy conservation

Total kinetic energy = total potential energy

So $2450+12=0+49\times 9.8\times h$

$h=5.127m$