Question

An athlete runs $300$ metres up a hill at a steady speed of $3.0$ m/s.
She then immediately runs the same distance down the hill at a steady speed of $6.0$ m/s.
What is her average speed for the $600$ metre run?

• A. $2.0$ m/s
• B. $3.0$ m/s
• C. $4.0$ m/s
• D. $4.5$ m/s

Answer 1

The correct option is C $4.0$ m/s

First part of motion :

Distance travelled, $s_1=300m$

Speed during the motion , $v_1=3.0m/s$
Time taken , $t_1=\frac{300}{3.0}=100s$

Second Part of motion :

Distance travelled, $s_2=300m$

Speed during the motion , $v_2=6.0m/s$
Time taken , $t_2=\frac{300}{6.0}=50s$

Average speed of athlete ,$V_{avg}=\frac{\text{Total distance travelled}}{\text{Total time taken}}=\frac{600}{t_1+t_2}=\frac{600}{100+50}=\frac{600}{150}=4.0m/s$