Question

In a slider–crank mechanism, the crank rotates at 60 rpm. The crank radius is 30 mm and the connecting rod length is 120 mm. The average speed (in mm/s) of the piston over one revolution of the crank is \(\underline{\hspace{2cm}}\) (round off to nearest integer).

Hint:

For average piston speed, only the total stroke travel per revolution matters—details of slider–crank geometry affect instantaneous speed, not average speed.

Answer 1

Correct Answer: 119 - 121

Crank radius: \[ r = 30\ \text{mm} \] Stroke length of piston: \[ \text{Stroke} = 2r = 60\ \text{mm} \] One full revolution causes one forward and one backward stroke. Total travel per revolution: \[ \text{Travel} = 2 \times 60 = 120\ \text{mm} \] Crank speed: \[ 60\ \text{rpm} = 1\ \text{rev/s} \] Average piston speed: \[ V_{\text{avg}} = \text{travel per rev} \times \text{rev/s} = 120 \times 1 = 120\ \text{mm/s} \] Rounded to nearest integer: \[ 120\ \text{mm/s} \]