On the graph of position versus time given below state (a) At which of the indic

Question

On the graph of position versus time given below state (a) At which of the indicated times the velocity is constant? (b) at which times the velocity is positive? (c) At which times the velocity is negative? (d) At which times the velocity is zero? (e) At which times the acceleration is positive? (f) At which times the acceleration is negative? (g) At which times the acceleration is zero? A delivery man travels 35 mi northwest to his first stop, 60 mi in a direction 35 degree west of south to his second stop. He then travels 10 mi to his final destination. What is the magnitude and direction of his displacement from his starting point? A car is traveling at 80 km/hr in a school zone. A police car is at rest in the parking lot of the school. The policeman begins accelerating as the speeder passes him with an acceleration of 8 m/sec^2. (a) How far has each car traveled when the police car catches the speeder? (b) How fast is the police car going when it catches the speeder? (c) Make a sketch of the position of both cars as a function of time? A crane is lowering a steel girder to the ground at a rate of 5 m/sec. When the girder is at a height of 40 m above the ground the cable breaks. How long does the person standing beneath the girder have to get out of the way? A shot-putter throws the shot with an initial speed of 16 m/sec at an angle of 35 degree to the horizontal. The shot is thrown from a height of 2 m. Find the horizontal distance the shot travels.

Explanation / Answer

Ans 45)

a) at constant velocity slope becomes linear

so velocity is constant at t2-t3 , t3-t5, t5-t6

b)

velocity is positive for positive slopes i.e t3-t5

c)

velocity is negative for negative slopes i.e.

t2-t3, t5-t6

d) velocity becomes zero when x doesent change with time i.e when graph is constant

0-t1, t7 and beyond

e)acceleration is positive when velocity chages from -ve to positive

at t3

f) acceleration is negative when velocity goes from positive to negative i.e. at t5

g) acceleration is zero when either velocity is 0 or velocity is constant

i.e from 0-t1, t7 and beyond , t2-t3 , t3-t5, t5-t6

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