Explanation:
Given parameters:
Initial velocity = 72km/hr
Final velocity = 0km/hr
Time taken = 25s
Unknown:
Acceleration = ?
Solution:
To solve this problem, convert km/hr to m/s;
1000m = 1km
3600s = 1hr
72km/hr;
1km/hr = 0.278m/s
72km/hr = 0.278 x 72 = 20.02m/s
Acceleration is the change in velocity divided by the time taken;
Acceleration =
Acceleration =
= -0.8m/s
The car is actually decelerating at a rate of 0.8m/s
Answer:
man will move in opposite direction with speed

Explanation:
As we know that man is lying on the friction-less surface
so here net force along the surface is zero
so if we take man + stone as a system then net change in momentum of this system will become zero
so here we have


here we have



Answer: 13.2 seconds.
Explanation: using equation of motion; S= ut +1/2at² where u = initial velocity=0
S= distance travelled
a = acceleration due gravity
t= time.
1 foot = 0.305m so,
S= 2860 feet =872.3m
S= ut+1/2 at²
872.3 = 0×t + 1/2×10 × t²
872.3 =0 + 5t²
T²= 872.3/5
T²= 174.46
Take the square root of T we then have;
t = 13.2 seconds to one decimal place.
Answer:

Explanation:
Given that,
Lightning flashes one mile (1609 m) away from you.
We need to find the time it take the light to travel that distance. Let the time be t. We know that,
speed = distance/time

So, the required time is 
I understand that sound travels faster in water then in air. Water is a liquid, and air is gas.
Water still has the ability to roll the molecules over each other (so water can flow), it has some flexibility.
But I do not understand how a solid that is inflexible can make sound waves travel faster then in a flexible liquid.
In fact, sound waves travel over 17 times faster through steel than through air.
Sound waves travel over four times faster in water than it would in air.