Question:

The motor pulls on the cable at A with a force F = a + ${ bt }^{ 2 }$. If the crate of weight W is originally at rest at t = 0, determine its speed at time t = ${ t }_{ 2 }$. Neglect the mass of the cable and pulleys. Hint: First find the time needed to begin lifting the crate. Given: W = 17 lb , a = 30 lb , b = ${ 1 lb/s }^{ 2 }$ , ${ t }_{ 2 }$ = 4 s