How Forces Affect Motion

A 5 kg block is acted on by a horizontal force of 30 N on a frictionless surface. The acceleration of the block is:

1. a\(3\ \text{m/s}^{2}\)
2. b\(12\ \text{m/s}^{2}\)
3. c\(6\ \text{m/s}^{2}\)
4. d\(30\ \text{m/s}^{2}\)

An object of mass 2 kg is moving with velocity 10 m/s. A force is applied for 4 s, increasing velocity to 18 m/s. The magnitude of the force applied is:

1. a2 N
2. b8 N
3. c6 N
4. d4 N

A 0.02 kg bullet is fired from a 4 kg gun. The gun pushes the bullet with a force of 10 N. What is the magnitude of the initial acceleration of the gun?

1. a\(500\ \text{m/s}^{2}\)
2. b\(2.5\ \text{m/s}^{2}\)
3. c\(0\ \text{m/s}^{2}\), because the two forces balance
4. d\(0.4\ \text{m/s}^{2}\)

Newton's first law of motion is also known as the law of:

1. aAction-reaction
2. bConservation of energy
3. cInertia
4. dAcceleration

Two boxes of masses 3 kg and 2 kg, joined by a string, lie on a frictionless horizontal surface. A horizontal force of 20 N pulls the 3 kg box. What is the acceleration of the two boxes?

1. a\(\dfrac{20}{3}\ \text{m/s}^{2}\)
2. b\(10\ \text{m/s}^{2}\)
3. c\(4\ \text{m/s}^{2}\)
4. d\(100\ \text{m/s}^{2}\)

A hammer of mass 1 kg moving at 10 m/s strikes a nail and is brought to rest in 0.01 s. The force exerted on the nail is:

1. a100 N
2. b10000 N
3. c10 N
4. d1000 N

The same stretched rubber band launches a stack of coins on a wooden table top, a laminated table top and a polished marble floor. On which surface does the stack travel the largest distance before stopping, and why?

1. aWooden table top, because the force of friction there is the largest
2. bPolished marble floor, because the force of friction there is the smallest
3. cLaminated table top, because the force of friction there is the smallest
4. dAll three the same, because the rubber band is stretched by the same amount

A 0.5 kg ball moving at 4 m/s is caught and brought to rest in 0.2 s. The force applied by the player's hand is:

1. a10 N
2. b5 N
3. c2 N
4. d20 N

Action and reaction forces:

1. aAct on the same object
2. bHave unequal magnitudes
3. cCancel each other on the same object
4. dAct on different objects

A car and a truck moving at the same speed collide head-on. Which is true regarding the FORCE experienced by each?

1. aBoth experience the SAME force (Newton's 3rd law)
2. bTruck experiences more force (larger mass)
3. cCar experiences more force (smaller mass)
4. dNeither experiences any force

Assertion (A): When a bus suddenly starts, passengers tend to fall backward.

Reason (R): When the bus accelerates forward, the lower part of the body moves with the bus while the upper part lags behind due to inertia of rest.

1. aBoth A and R are true, and R is the correct explanation for A
2. bBoth A and R are true, but R is NOT the correct explanation for A
3. cA is true, but R is false
4. dA is false, but R is true

Assertion (A): A heavier object requires more force than a lighter object to produce the same acceleration.

Reason (R): By Newton's second law, \(F = ma\); for the same acceleration, force is proportional to mass.

1. aBoth A and R are true, and R is the correct explanation for A
2. bBoth A and R are true, but R is NOT the correct explanation for A
3. cA is true, but R is false
4. dA is false, but R is true

Assertion (A): An object moving with a constant velocity must have a net force acting on it.

Reason (R): If the net force acting on an object is zero, its acceleration is zero.

1. aBoth A and R are true, and R is the correct explanation for A
2. bBoth A and R are true, but R is NOT the correct explanation for A
3. cA is true, but R is false
4. dA is false, but R is true

Assertion (A): A horse pulls a cart and the cart moves forward.

Reason (R): By Newton's third law, the force exerted by the horse on the cart is equal and opposite to the force exerted by the cart on the horse.

1. aBoth A and R are true, and R is the correct explanation for A
2. bBoth A and R are true, but R is NOT the correct explanation for A
3. cA is true, but R is false
4. dA is false, but R is true

1. I. I. The force of friction acts on an object in the direction opposite to its direction of motion.
2. II. II. A spring balance can measure the magnitude of a force in general, not only the weight of an object.
3. III. III. When several forces act on an object, its motion depends only on the largest of these forces.

Which of the statements above is/are correct?

1. aOnly II and III
2. bOnly I and II
3. cOnly I and III
4. dI, II and III

1. I. I. When a net force acts on an object, the object accelerates in the direction of the net force.
2. II. II. The acceleration due to the gravitational force by the Earth is larger for heavier objects.
3. III. III. Taking \(g = 9.8\ \text{m/s}^{2}\), the gravitational force on a 2 kg object is 19.6 N.

Which of the statements above is/are correct?

1. aOnly I
2. bOnly I and II
3. cOnly I and III
4. dI, II and III

1. I. The SI unit of force is newton; \(1\ \text{N} = 1\ \text{kg m/s}^{2}\).
2. II. Force is a vector quantity having both magnitude and direction.
3. III. An unbalanced force can change either the speed or the direction of motion (or both).

Which of the above statements about force is/are correct?

1. aI and II
2. bII and III
3. cI, II and III
4. dI and III

1. I. I. When you walk, the ground pushes your feet forward through the force of friction.
2. II. II. Newton's third law applies only to contact forces, such as a push or a pull.
3. III. III. A rocket lifts off because the gases it expels downwards push it upwards with a force larger than its weight.

Which of the statements above about Newton's third law is/are correct?

1. aOnly I and III
2. bOnly I and II
3. cI, II and III
4. dOnly I

Match List I (observation) with List II (its explanation):

1. a(i)-S, (ii)-Q, (iii)-R, (iv)-P
2. b(i)-Q, (ii)-S, (iii)-P, (iv)-R
3. c(i)-R, (ii)-S, (iii)-Q, (iv)-P
4. d(i)-Q, (ii)-S, (iii)-R, (iv)-P

Match List I (situation) with List II (the net force or force needed):

1. a(i)-Q, (ii)-R, (iii)-S, (iv)-P
2. b(i)-R, (ii)-Q, (iii)-S, (iv)-P
3. c(i)-R, (ii)-Q, (iii)-P, (iv)-S
4. d(i)-S, (ii)-Q, (iii)-R, (iv)-P

Match List I with List II:

1. a(i)-R, (ii)-S, (iii)-Q, (iv)-P
2. b(i)-P, (ii)-S, (iii)-Q, (iv)-R
3. c(i)-R, (ii)-Q, (iii)-S, (iv)-P
4. d(i)-Q, (ii)-S, (iii)-R, (iv)-P

Why does a fielder pull his hands back while catching a fast cricket ball?

1. aTo increase the force on the hands
2. bTo increase the velocity of the ball
3. cTo increase the time of impact, thereby reducing the impact force on the hands
4. dTo decrease the mass of the ball

A sailor standing in a small boat at rest jumps forward onto the shore. What happens to the boat as the sailor jumps?

1. aIt stays still, because the forces on the sailor and the boat cancel each other
2. bIt moves backward, because the sailor pushes it backward while it pushes the sailor forward
3. cIt moves backward only if the water is flowing
4. dIt moves forward along with the sailor

A 1000 kg car moving at 20 m/s applies brakes and stops in 5 s. The braking force is:

1. a2000 N
2. b10000 N
3. c8000 N
4. d4000 N

From the passage, why does the person in a moving train stay 'with' the train rather than feeling pushed?

1. aThe train has no friction
2. bAir pushes the person along
3. cThe train compensates for inertia
4. dThe person's body has the same velocity as the train (inertia of motion); no relative motion is felt

From the passage, when the train suddenly brakes, the person lurches forward because:

1. aThe train accelerates
2. bThe train decelerates but the person's body, by inertia, continues at the original velocity briefly
3. cFriction reverses direction
4. dGravity acts forward

From the passage, the safety strap (harness) helps by:

1. aAdding mass to the person
2. bReducing inertia
3. cProviding a force that decelerates the person along with the vehicle, preventing forward thrust
4. dRemoving friction

Suppose the same braking force acts on two otherwise identical trains like Aman's, one full of passengers and one empty (ignore all other forces). Which train slows down with the smaller deceleration?

1. aThe loaded train, because the same force gives a larger mass a smaller acceleration
2. bBoth trains equally, because equal braking forces always give equal decelerations
3. cThe empty train, because a smaller mass needs a smaller force to be stopped
4. dIt cannot be decided without knowing the speeds of the two trains

Two bodies of masses 1 kg and 4 kg have the same momentum. The ratio of their velocities (\(\dfrac{v_{1}}{v_{2}}\)) is:

1. a4:1
2. b1:4
3. c2:1
4. d1:2

If a force \(F\) applied for time \(t\) on a body of mass \(m\) produces velocity \(v\) starting from rest, then for the SAME body the velocity after applying force \(2F\) for time \(\dfrac{t}{2}\) starting from rest is:

1. a\(\dfrac{v}{2}\)
2. b\(v\)
3. c\(2v\)
4. d\(4v\)