Please help with this question

Question

Question 4

To serve in tennis, a player throws the ball upwards and then hits the ball with a racquet so that the ball bounces on the other side of the net. The height, x metres, of the ball above the ground at time t seconds after it is thrown up can be modelled by:

x(t) 1000*t^3+1700*t^2 + 630t + 81

1. a) What is the height of the ball when it leaves the player’s hand? Give the answer correct to the nearest centimetre.
2. b) What is the greatest height reached by the ball, correct to the nearest centimetre.

Answer 1

The student might have to convert the units but I suggest that the student double-checks the original question.

For 1a) we want to find the height of the ball before it leaves the player's hand. So how many seconds "t" have gone by since the player threw the ball? Well, imagine if the player didn't throw the ball, and our timer begins once the ball is thrown. Since the ball didn't move out of the players' hand the timer did not start. Thus the time that went by is 0 seconds. We can now substitute t=0 seconds to the original equation because x(t) represents the height of the ball at a specific time"t"

x(t)= 1000*t^3+1700*t^2 + 630t + 81

x(0)= 1000*t(0)^3+1700*t(0)^2 + 630(0) + 81

Continue the problem :)