Answer :
1). The 'acceleration due to gravity' is about 9.8m/s². That means
that the downward speed of a a falling object increases by 9.8 m/s
every second it falls.
The egg was thrown downward at 10 m/s, and was falling at 25 m/s
when it went splat on the ground. Gravity increased its speed by
(25 - 10) = 15 m/s. That takes (15/9.8) = 1.53 seconds.
2). The 'acceleration due to gravity' is about 9.8m/s². That means
that the downward speed of a a falling object increases by 9.8 m/s
every second it falls.
After falling for 2.5 sec, its downward speed is (2.5 x 9.8) = 24.5 m/s
faster than it was when the object began falling.
3). The 'acceleration due to gravity' is about 9.8m/s². That means
that the downward speed of a a falling object increases by 9.8 m/s
every second it falls.
(Have you noticed a pattern among these questions yet ?)
Acceleration = (change of speed) / (time for the chage).
change of speed = (end speed) minus (start speed) = (25m/s - start speed).
Acceleration = (25m/s - start speed) / (time for the change)
1.5 m/s² = (25m/s - start speed) / (10 sec)
Let's multiply each side by 10sec : 15 m/s = 25m/s - start-speed
Add start-speed to each side: start-speed + 15 m/s = 25 m/s
Subtract 15 m/s from each side: Start-speed = (25-15) m/s = 10 m/s
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Quicker & easier way:
(Caution ... requires thinking)
Accelerate uniformly at 1.5 m/s² for 10 sec ===> gain 15 m/s of speed
Moving at 25 m/s after gaining 15m/s ===> must have started out at 10m/s.
