A ball is thrown upward and its height after t seconds is h = 20t - 5t^2 metres. Setting h = 15 gives 5t^2 - 20t + 15 = 0. Using the formula, the first time the ball is 15 m above the ground is:

Question

Accepted Answer

1 s. Divide by 5: t^2 - 4t + 3 = 0. D = 16 - 12 = 4, √D = 2. t = 4 ± 2/2 = 3 or 1. Both times are valid (going up at t = 1 s, coming down at t = 3 s); the first is 1 s.

A ball is thrown upward and its height after $t$ seconds is $h = 20 t - 5 t^{2}$ metres.
Setting $h = 15$ gives $5 t^{2} - 20 t + 15 = 0$ . Using the formula, the first time
the ball is 15 m above the ground is:

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More Class 10 The Quadratic Formula practice

A ball is thrown upward and its height after t seconds is h=20t−5t2 metres.Setting h=15 gives 5t2−20t+15=0. Using the formula, the first timethe ball is 15 m above the ground is:

Step-by-Step Solution

Master this chapter in 30 minutes a day.

More Class 10 The Quadratic Formula practice

A ball is thrown upward and its height after $t$ seconds is $h = 20 t - 5 t^{2}$ metres.
Setting $h = 15$ gives $5 t^{2} - 20 t + 15 = 0$ . Using the formula, the first time
the ball is 15 m above the ground is: