The first thing you should know for this case is that density is defined as the quotient between mass and volume: D = M / V In addition, you should keep in mind the following conversion: 1Kg = 1000g Substituting the values we have: D = (23.0 * 1000) / (2920) = 7.88 g / cm ^ 3 answer the density of the iron plate is 7.88 g / cm ^ 3
Finding out the acceleration 12/3 = 4m/s^2 thus it is descending so the actual acceleration would be 9.8-4 = 5.8 m/s^2 the weight will be 90*5.8 = 522 N 522/9.8 = 53.2 kg