Question

4. An object is released from rest from the top of a tall building. Use g 9.8 m/sec?. Ignore air resistance. a) What is the speed of the object 1 second after it is released? 3 seconds after it is released? b) The building is 100 m tall. How many seconds will it take for the object to reach the ground? c) What is the speed of the object just as it hits the ground? 5. A car has an initial velocity of 10 m/s. It undergoes an acceleration of 1.5 m/sec2 for 4 seconds then an acceleration of-2 m/sec2 for 6 seconds a) Draw a motion diagram. There are two parts. Include the acceleration vector for each part b) What is the final velocity of the car?
Please answer all of the questions and circle your answers

Answer 1

(a) object is relaes3ed from rest so, initial velocity = u = 0m/s acceleration = g = 9.8m/s using v = 4 + gt v = 0 +(9.8)(1) v = 9.8m/s implies speed after 1sec v = 9.8m/s similarly speed after 3sec v = u + gt v = 0 + 9.8 times 3 v = 29.4 m/s (b) height = 100m so distance travelled by object after reaching ground = s = 100m now using s = ut + 1/2 gt^2 100 = a(t) + 1/2 (9.8)t^2 100 times 2/9.8 = t^2 t = squareroot 100 times 2/9.8 t = 4.517sec time taken by object to reach ground (c) let the speed of object just as it hit the ground be v m/s using v^2 = u^2 + 2gh v^2 = (0)^2 + 2 times 9.8 times 100 v = squareroot 2 times 9.8 times 100 v = 44.27m/s given initial velocity g as = u = 10m/s acceleration = a = 1.5m/s^2 for 4sec & a = -2m/s^2 for 6sec (a) motion diagram (b) for t = 4sec velocity = v = u + at = 10 + 1.5(4) = 10 + 6 = 16m/s this velocity will acts a initial velocity