## Essential University Physics: Volume 1 (3rd Edition)

a) $m = 7.065 kg$ b) $m = 3.947 kg$
a) We assume that the pulley is massless. We know that the left mass is 2.1 kg. Thus, we treat this as a system, and we use Newton's second law to find: $-.64(m+2.1)=2.1gsin60-mgsin20\\ m = 7.065 kg$ b) We use a similar process to find: $.76(m+2.1)=2.1gsin60-mgsin20\\ m = 3.947 kg$