Question

A child pulls a string attached to a toy car with a constant force of 7.8 N. The toy car accelerates from
rest to 3 m/s in 1.2 s. What is the mass of the toy car?
A. 3.12 kg
B. 2.6 kg
C. 0.38 kg
D. 0.32 kg

Answer 1

By Newton's second law, the car has mass m so that the net force is

∑ F = ma

Find the acceleration a of the car. Since the force is constant, acceleration is also constant. If the car accelerates from rest to 3 m/s in 1.2 s, then its acceleration is

a = (3 m/s - 0) / (1.2 s) = 2.5 m/s²

Then the mass of the car m is such that

7.8 N = m (2.5 m/s²)

Solve for m :

m = (7.8 N) / (2.5 m/s²) = 3.12 kg