Question

A heavy steel cable attached to a motor is lifting a girder. The girder is speeding up.

Answer 1

Answer: part a) both the tension and gravity vectors will be pointing downwards.

part b) the tension vector will be pointing upwards and the gravity will be pointing downwards.

Explanation:

part a) Since you are looking at the FBD for the steel cable here, the tension will be pointing downwards because the girder is hung from the cable which creates a downwards tension. Gravity will always point downwards, to the ground.

part b) Since you are looking at the FBD for the girder here, the tension will be pulled upwards because the cable is weighted which creates an upwards tension. Gravity will always point downwards, to the ground.

Sorry for the poor explanation, but hopefully this makes sense.