Advertisements
Advertisements
प्रश्न
A constant retarding force of 50 N is applied to a body of mass 20 kg moving initially with a speed of 15 ms–1. How long does the body take to stop?
Advertisements
उत्तर १
Retarding force, F = –50 N
Mass of the body, m = 20 kg
Initial velocity of the body, u = 15 m/s
Final velocity of the body, v = 0
Using Newton’s second law of motion, the acceleration (a) produced in the body can be computed as follows:
F = ma
–50 = 20 × a
`:. a = (-50)/20 = -2.5 "m/s"^2`
The first equation of motion allows for the calculation of the body's time (t) to come to rest as follows:
v = u + at
`:. t = (-u)/a = (-15)/(-2.5) = 6 s`
उत्तर २
Here m = 20 kg, F = – 50 N (retardation force)
As F = ma
`=> a = F/m = (-50)/20 = -2.5 ms^(-2)`
Using equation v = u + at
Given `u = 15 ms^(-1), v = 0`
Now, 0 = 15 + (-25) t
or t = 6 s
APPEARS IN
संबंधित प्रश्न
Two masses 8 kg and 12 kg are connected at the two ends of a light, inextensible string that goes over a frictionless pulley. Find the acceleration of the masses, and the tension in the string when the masses are released.
A helicopter of mass 1000 kg rises with a vertical acceleration of 15 m s–2. The crew and the passengers weigh 300 kg. Give the magnitude and direction of the
(a) force on the floor by the crew and passengers,
(b) action of the rotor of the helicopter on the surrounding air,
(c) force on the helicopter due to the surrounding air.
Suppose the ceiling in the previous problem is that of an elevator which is going up with an acceleration of 2.0 m/s2. Find the elongation.
A force \[\vec{F} = \vec{v} \times \vec{A}\] is exerted on a particle in addition to the force of gravity, where \[\vec{v}\] is the velocity of the particle and \[\vec{A}\] is a constant vector in the horizontal direction. With what minimum speed, a particle of mass m be projected so that it continues to move without being defelected and with a constant velocity?
Find the acceleration of the blocks A and B in the three situations shown in the following figure.
A monkey is climbing on a rope that goes over a smooth light pulley and supports a block of equal mass at the other end in the following figure. Show that whatever force the monkey exerts on the rope, the monkey and the block move in the same direction with equal acceleration. If initially both were at rest, their separation will not change as time passes.
A tennis ball and a cricket ball , both are stationary. To start motion in them .
State the Newton's second law of motion. What information do you get from it?
A stone is dropped freely from the top of a tower and it reaches the ground in 4 s. Taking g = 10m s-2, calculate the height of the tower.
A body of mass 200 g is moving with a velocity of 5 ms−1. If the velocity of the body changes to 17 ms−1, calculate the change in linear momentum of the body.
A motorcycle of mass 100 kg is running at 10 ms−1. If its engine develops an extra linear momentum of 2000 Ns, calculate the new velocity of a motorcycle.
Name the physical quantity which equals the rate of change of linear momentum.
What do you mean by an impulsive force?
Use Newton's second law to explain the following:
While catching a fast moving ball, we always pull our hands backwards.
A stone is dropped from a cliff 98 m high.
What will be its speed when it strikes the ground?
A ball is thrown vertically downward with an initial velocity of 10 m/s. What is its speed 1 s later and 2 s later?
A stone is dropped from a tower 98 m high. With what speed should a second stone be thrown 1 s later so that both hit the ground at the same time?
In the previous problem (5.3), the magnitude of the momentum transferred during the hit is ______.
According to Newton's Second Law of Motion, what quantity is directly proportional to the applied force?
What happens when a car brakes to come to a stop?
