Advertisements
Advertisements
Question
The driver of a three-wheeler moving with a speed of 36 km/h sees a child standing in the middle of the road and brings his vehicle to rest in 4.0 s just in time to save the child. What is the average retarding force on the vehicle? The mass of the three-wheeler is 400 kg and the mass of the driver is 65 kg.
Advertisements
Solution
Initial speed of the three-wheeler, u = 36 km/h
= 36 × (5/18) m/s
= 10 m/s
Final speed of the three-wheeler, v = 0 m/s
Time, t = 4 s
Mass of the three-wheeler, m = 400 kg
Mass of the driver, m' = 65 kg
Total mass of the system, M = 400 + 65 = 465 kg
Using the first law of motion, the acceleration (a) of the three-wheeler can be calculated as:
v = u + at
`:. a =(v-u)/t = (0 - 10)/4 = -2.5 "m/s"^2`
The negative sign signifies that the velocity of the three-wheeler is reducing over time.
Using Newton’s second law of motion, the net force acting on the three-wheeler can be calculated as:
F = Ma
= 465 × (-2.5) = -1162.5 N = 1.2 × 103 N
The negative sign suggests that the force is applied in opposition to the direction of motion of the three-wheeler.
APPEARS IN
RELATED QUESTIONS
The force exerted by the floor of an elevator on the foot of a person is more than the weight of the person if the elevator is
(a) going up and slowing down
(b) going up and speeding up
(c) going down and slowing down
(d) going down and speeding up
A block of mass 2 kg placed on a long frictionless horizontal table is pulled horizontally by a constant force F. It is found to move 10 m in the first seconds. Find the magnitude of F.
When a train starts, the head of a standing passenger seems to be pushed backward. Analyse the situation from the ground frame. Does it really go backward? Coming back to the train frame, how do you explain the backward movement of the head on the basis of Newton's laws?
'When a hanging carpet is beaten with a stick, the dust particles start coming out of it'. This phenomenon can be best explained by making use of :
State Newton's first law of motion.
State and explain the law of inertia (or Newton's first law of motion).
How does Newton's second law of motion differ from the first law of motion?
A force of 600 dynes acts on a glass ball of mass 200 g for 12 s. If initially, the ball is at rest, find
- Final velocity
- Distance covered.
What do you mean by inertia of motion?
Give one example each of inertia of rest and inertia of motion.
The greater is the __________ the greater is the inertia of an object.
A man riding on a car has ___________ Inertia.
What do you mean by inertia of rest?
Give two examples of the following:
Inertia of motion
If a 5 N and a 15 N forces are acting opposite to one another. Find the resultant force and the direction of action of the resultant force.
When a bus suddenly takes a tum, the passengers are thrown outwards because of
Newton's first law of motion describes ______.
A smooth sphere of radius R and mass M is placed on the smooth horizontal floor. Another smooth particle of mass m is placed on the sphere and a horizontal force F is applied on the sphere as shown. If the particle does not slip on the sphere then the value of force F is ______.
A balloon has mass of 10 g in air. The air escapes from the balloon at a uniform rate with velocity 4.5 cm/s. If the balloon shrinks in 5 s completely. Then, the average force acting on that balloon will be (in dyne).
How is force defined according to Newton’s First Law?
