Advertisements
Advertisements
प्रश्न
A car is travelling at 20 m/s along a road. A child runs out into the road 50 m ahead and the car driver steps on the brake pedal. What must the car’s deceleration be if the car is to stop just before it reaches the child ?
Advertisements
उत्तर
We have to find the deceleration. We have the following information given,
Initial velocity, (u) = 20 m/s
Final velocity, (v) = 0 m/s
Distance travelled, (s) = 50 m
Let the deceleration for the entire journey be (a)
We can calculate acceleration by using the 3rd equation of motion,
`a = (v^2-u^2)/(2s)`
(s) - Displacement
(u) - Initial velocity
(a) - Acceleration
(v) - Final velocity
Put the values in above equation to find the deceleration,
`a = [(0-400)/(2(50)]] "m/s"^2`
= `(-400/100)` `"m/s"^2`
= -4 `"m/s"^2`
Hence, deceleration is 4 m/s2.
APPEARS IN
संबंधित प्रश्न
What can you say about the motion of an object whose distance-time graph is a straight line parallel to the time axis?
A driver of a car travelling at 52 km h−1 applies the brakes and accelerates uniformly in the opposite direction. The car stops in 5 s. Another driver going at 3 km h−1 in another car applies his brakes slowly and stops in 10 s. On the same graph paper, plot the speed versus time graphs for the two cars. Which of the two cars travelled farther after the brakes were applied?
What does the slope of a distance-time graph indicate ?
What can you say about the motion of a body whose distance-time graph is a straight line parallel to the time axis ?
Fill in the following blank with suitable word :
The slope of a distance-time graph indicates ………………….. of a moving body.
A cyclist is travelling at 15 m s-1. She applies brakes so that she does not collide with a wall 18 m away. What deceleration must she have ?
Two friends leave Delhi for Chandigarh in their cars. A starts at 5 am and moves with a constant speed of 30 km/h, whereas B starts at 6 am and moves with a constant speed of 40 kmh-1. Plot the distance-time graph for their motion and find at what time the two friends will meet and at what distance from Delhi.
Boojho goes to the football ground to play football. The distance-time graph of his journey from his home to the ground is given in the figure.
- What does the graph between points B and C indicate about the motion of Boojho?
- Is the motion between 0 to 4 minutes uniform or non-uniform?
- What is his speed between 8 and 12 minutes of his journey?
Assertion: The position-time graph of a uniform motion in one dimension of a body can have a negative slope
Reason: When the speed of the body decreases with time then, the position-time graph of the moving body has a negative slope.
What do you infer if
- Distance – time graph is a straight line.
- The velocity-time graph is curved.
- Displacement time is zigzag.
