NEWTON`S LAW OF MOTION
Q-Explain why a cricketer moves his hands backwards while holding a catch.
A-A cricketer moves his hand to increase the impact of the ball that is shot by the batsman, so that the force of the ball gets reduced to a comfortable limit without causing injury to the hands.
Q-If the mass of a bus is 2000 kg, what will the force required to speed up a bus at the 6ms–2?
A-According to the question:
Acceleration (a) = 6m/s2 and Mass (m) = 2000 kg, therefore, Force (F) =?
According to the formula, F = m x a
= 2000 kg x 6m/s2
= 12000 kg m/s2
It means , required Force is = 12000 N
Q-Name the factor on which coefficient of friction depends?
A-The coefficient of friction will mainly depends upon two factor, they are as following:
- The materials of the surfaces in contact.
- The characteristics of the surfaces.
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Q- Why does a swimmer push the water backwards?
A- We know that “when one body exerts a force on the other body, the first body experiences a force equivalent in magnitude in the opposite direction of the force exerted” because of Newton’s third law of motion. Consequently, the swimmer uses his hands to push water backward in order to swim ahead.
Q-A person driving a car suddenly applies the brakes on seeing a child on the road ahead. If he is not wearing a seat belt, he falls forward and hits his head against the steering wheel. Why?
A-When a person applies brakes suddenly, he tends to fall forward and hit his head against the steering wheel if he is not wearing the seat belt because his upper body continues to be in a state of motion and in the same direction as that of the car which is due to the inertia of motion.
Q-Why are mountain roads generally made winding upwards rather than going straight up? –
A-The mountain roads are generally made winding upwards rather than going straight up because the force of friction is high which reduces the chances of skidding. When the roads are straight up, the value of frictional force increases which increases the chance of skidding. This is given by:
fs = μN cosθ where θ is the angle of inclination.
Q-There are three forces P1, P2, and P3, acting on a body, all acting on a point A on the body. The body is found to move with uniform speed.
a) show that the forces are coplanar
b) show that the torque acting on the body about any point due to these three forces is zero
A-a) Acceleration of the body is zero as the three forces P1, P2, and P3 on a point on a body have a resultant force equal to zero. The direction of forces P1 and p2 are in the plane of the paper and in their sum is in the opposite direction in the same plane. Also, P3 is in the same plane. Therefore, all the three forces are coplanar.
b) The resultant of forces P1, p2, and P3 are zero and the torque is also equal to zero. That is, the resultant force is given as:
P = P1 + P2 + P3 = 0.
It means , we can say that at any point, the torque acting will be zero.
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Q-A man jumping out of a moving train falls with his head forward. Why?
A-As the man jumps out from a moving train, his feet suddenly come to rest on touching the ground while the upper part of his body continues to move forward. That is why he falls with his head forward. In order to save himself, he should run through some distance in the forward direction.
Q-A force of 50N act on the object of mass 20 kg. shown in the figure. Calculate the acceleration of the object in x and y directions.
A- Watch video solution. click below.
Q-A spider of mass 50 g is hanging on a string of a cob web as shown in the figure. What is the tension in the string?
A- According to question T = mg
Mass (m) = 50g = 0.050 kg
g = 9.8 ms-2
T = 0.050 × 9.8
= 0.49 N.
Ans: T=0.49N
Q-A car takes a turn with velocity 50 m s-1 on the circular road of radius of curvature 10 m. Calculate the centrifugal force experienced by a person of mass 60kg inside the car.
A- watch video solution. click below.