Instructor: Dr. Amit Chakrabarti, CW 213, Tel: 532-1625.
2. a = net force / m = 2 N /2 kg = 1 m/s/s/.
3. Forces from the engines are acting in the same direction, so they add up. So the total net force is 4 x 30,000 N = 120,000 N. Now, a= net force / mass = 120,000 N /30,000 kg = 4 m/s/s/.
4. The reaction force of the wall onto you is also 30 N. your acceleration is given by a = net force on you / mass = 30 N /60 kg = 0.5 m/s/s/.
5. This problem is like the bike problem I worked out in class. We know net force = mass x acceleration. So the net force acting on the firefighter is = 80 kg x 4 m/s/s/= 320 N, downwards. This net force comes from two contribution; force of gravity (= firefighter's weight) downwards and the friction force acting upwards. The firefighter's weight is (w=mg) = 80kg x 9.8 m/s/s = 784 N and this is the force acting downwards. So we find 784N, downwards - friction force, upwards = net force of 320 N, downwards. This means the friction force is 464 N, upwards.